There are many practices that certain laity and priests, of their own authority, have introduced into the Catholic liturgy that find no precedent in two thousand years of Christian Tradition. Yet, if questioned on the justification for these practices, their adherents will often cite examples out of the Bible. A common example is David dancing before the Ark as justification for liturgical dancing; a new one I encountered recently is the practice in charismatic parishes of people taking their shoes off and going about barefoot in the sanctuary, even in the immediate presence of the Blessed Sacrament. The argument in favor of this behavior is that it calls to mind the intimacy God wishes to have with us, as well as the example of Moses, who when coming into God's presence, was told to remove his sandals. Based on these considerations, this practice of going about in the sanctuary barefoot is considered praiseworthy and not irreverent in the least. Yet, as we shall see, the practice is based on an errant approach to the Bible and liturgy that wrongly assumes that it is acceptable to lift liturgical practices directly from things we read in the Bible without reference to the Church's Tradition.
For the sake of this article, we will keep coming back to the example of walking around barefoot in in the sanctuary, although the arguments we will put forth can be applied to a variety of behaviors.
Intimacy and Boundary
At the outset, we must admit that it is certainly true that our Lord desires intimacy with us. As St. Augustine noted, He is closer to us than we are to ourselves, and wishes us to depend upon Him more than we depend upon the air we breathe. Furthermore, by the death of Jesus Christ, we have access to the Father and are invited to seek Him as a treasure. This is why Scripture admonishes us to "go with confidence to the throne of grace that we may obtain mercy, and find grace in seasonable aid" (Heb. 4:16), or, as common Protestant Bibles have it, "come boldly before the throne of grace."
Let us begin by pointing out that the call to intimacy does not mean a license to undue familiarity. Intimacy does not mean that all boundaries of propriety are removed; intimacy is defined by as a relationship where the two persons share affection; another definition states that intimacy consists in "a close association with or detailed knowledge or deep understanding."  Neither definition, nor its Latin root intimatus ("close association"), suggest a dissolution of boundaries. In fact, it could be said that the essence of intimacy is affection and knowledge to the fullest extent within a given set of boundaries.
For example, I have a friend named Jonathan. I have known him for twenty years. We have an intimate friendship and know almost everything about one another and, as far as I can tell, this friendship will continue to grow and mature for the rest of our lives. Yet, no matter how long we have known one another, I cannot imagine a situation where it would be alright for me to watch him go to the bathroom; despite our association, if I were to go into his home and start clipping my toenails, he would rightly feel that I had transgressed some boundary, as I would if he were to do so in my house. Despite our intimacy, there are still boundaries, and this is true even of husbands and wives. The intimate nature of marriage does not mean that all boundaries are dissolved and everything is licit; if anything, the married state means that we have to be extra sensitive of what is and is not appropriate behavior with our spouses so that we can love them as Christ intended and not treat them basely by presuming that they have no boundaries we need respect.
We have been discussing this on a natural level, but of course this is relevant on a supernatural level. God of course wants us to have intimacy with Him, but it is nowhere suggested in Scripture that he wants an undue familiarity with no boundaries whatsoever. When Scriptures encourage us to "go with confidence to the throne of grace", they are referring to the interior disposition proper to prayer, not endorsing any particular outward activity or throwing out the need for proper boundaries. The fact that God wants us to approach Him "with confidence" no more suggests the taking off of shoes at Mass than the verse "look up for your redemption draws near" suggests that we should crane our necks to the sky. Both verses refer to our interior dispositions and do not mandate any act, nor release us from the rules of proper behavior.
There is a bit of an interplay between grace and nature here. By grace, God has made us His children and calls us to communion with Him, and hence we make our petitions known, "boldly" pray Our Father, and receive Him in Holy Communion- all of this made possible by grace. Yet, though the adoption by grace puts us into a state of sonship, the distinction between creature and Creator is never obliterated. Sons or no sons, when a human being approaches God, it is always approaching a Mystery more powerful and glorious than anything else in the universe. This is why, though we "have the courage" to say "Our Father," we still bow our knee before the Presence of a mystery we don't understand, and take care that Communion is received with the maximal amount of reverence.
Note the relation between intimacy and boundary: the moment of Holy Communion, which is meant to be the most intimate, is also the moment where the boundary between layman and priest, and man and God, is most profound. But the observation of these profound boundaries do not diminish intimacy; on the contrary, the intimacy of the moment of Holy Communion is established by a keen awareness and sensitivity to the boundaries surrounding this sublime moment when God comes to meet man.
In our culture, the act of going barefoot never suggests anything other than extreme casualness. We go barefoot when it is nice enough outside to wear we don't have to wear shoes, when we are bumming around the house and have not gotten dressed yet (or have undressed at the end of the day), or when we are on terms of extreme familiarity with someone and can come into their house and kick our sandals off. These actions all suggest a crass informality or casualness that does not respect the mysterious boundary between creature and Creator. Regardless of what people say the act might mean, the body and the things we do with it suggest certain things, whether we mean them to or not - and what is suggested by walking around barefoot in the sanctuary and in the presence of the Blessed Sacrament is not reverence. We would never show up to an appointment with any other human being barefoot; why then the King of the Universe?
Liturgical Decorum and the Bible
It seems that people get confused on this because of the issue of decorum, meaning what is fitting for liturgical settings. The liturgy and the sanctuary of the Church have their own decorum that are appropriate to them, as understood and interpreted through two millennia of Christian Tradition. This corpus of decorum (everything from the practice of genuflecting to the sorts of art and architecture proper for worship) comes to us through Tradition and is in many cases made binding by the disciplinary instruction of the Magisterium.
Here is where people get confused: what is proper decorum for the liturgy may be informed and supported by biblical examples, but biblical examples themselves do not establish liturgical decorum. This point is of utmost importance; we do not take what we read in the Bible and mimic it in our liturgies; what we read may inspire or inform what happens in liturgy, but liturgy itself is based on a living Tradition passed on through the ages of the Church and interpreted by the Magisterium. It is something passed on that is alive; it is not simply taken from the Bible.
This is why not everything we read in the Bible is appropriate in a liturgical setting. A classic example is David dancing before the Ark of the Covenant. If we had a liturgical decorum in which what we did at Mass was lifted straight from the pages of Scripture, we should allow liturgical dancing, since King David set a very clear precedent for it. But in fact liturgical dancing is not and has never been allowed at Mass in the Latin rite; in fact, it is considered liturgical abuse, and the fact that King David danced in a moment of prophetic inspiration during a procession does not mean the same action is fitting for a Catholic liturgy (see here for more on the issue of David dancing). By the way, to establish this point further, it should be pointed out that there are many Protestant groups who do in fact take their practice directly from the Bible and do sanction liturgical dancing because of David's precedent.
In the case of going barefoot in front of the Blessed Sacrament, the fact that we read of Moses being told to take his shoes off in the presence of God should similarly not be taken as a liturgical instruction. If we take this command that was given to Moses in the context of a theophany on the top of a mountain as an instruction for how we are to conduct liturgy or approach God in worship, why not also utilize God's command to Isaiah to walk naked for three years, or his command to Ezekiel to shave off all his hair, or Hosea to marry a prostitute, or for Abraham to cut a bunch of birds in half and lay them in pieces on the ground? (Isa. 20:2-3, Ezk. 5:1-12, Hos. 1, Gen. 9:10-11). The fact that we see a behavior displayed in the Bible does not mean it is fitting for liturgy.
Liturgical Behavior vs. 'Theophantic Behavior'
Here we could posit a distinction between liturgical behavior and what I call 'theophantic behavior'; that is, how we behave when encountering God through the liturgical acts of the Church as opposed to how human beings have acted when encountering God in a powerful supernatural manifestation. In the Bible, theophanies are usually powerful manifestations of God's power made privately to individuals for the sake of delivering a message or empowering them to carry out some act willed by God. In a theophany, humanity comes into direct contact with the divine, and how people will behave is anybody's guess. They may take their shoes off (Ex. 3); they may throw themselves to the ground and act as if dead (Rev. 1:17); their face may glow supernaturally (Ex. 34:29), they may float into the air or fall into a trance for hours, as is reported of various saints; they may cry out spontaneously in adoration (Luke 1), well up in song (Ex. 15:1-18), or they may be overcome with terror and fear (Gen. 15:12), or they may babble because they do not know what else to say, as Peter did on the Mount of Transfiguration ("Peter said to him, 'Master, it is good for us to be here. Let us put up three shelters—one for you, one for Moses and one for Elijah.' He did not know what he was saying." [Luke 9:33]). Humanity may, in some circumstances, be struck dead in the presence of God (2 Sam. 6:1-10, Lev. 10:1).
These are all common or at least documented examples of how human beings respond when they confront the divine in a supernatural manifestation; these are what I term 'theophantic behaviors.' Yet would anyone suppose that these behaviors, such as falling down as if dead and crying out spontaneously, are acceptable for liturgical worship? Surely not. If we had people falling into trances, crying out in adoration or terror, babbling, singing as the spirit moves them, floating, taking various articles of clothing off, etc., then liturgy as a formal, public act of worship would have no real meaning. In short, the behaviors that may flow out spontaneously when an individual encounters God supernaturally in a private revelation do not automatically translate to being acceptable as the formal worship of the congregation encountering God sacramentally in a public act of worship. Liturgical worship, in which God is encountered through mystery in the Church's sacramental rites, demands a different decorum than situations where God is encountered directly and supernaturally without the veil of sacramental signs.
if we understand this distinction between liturgical and 'theophantic' responses, then the argument that certain behaviors we note in the Scripture are appropriate for the Catholic liturgy really falls apart. Remember, the biblical examples may inspire liturgical actions or give them symbolic value - the cries of the angels in Isaiah 6 are found in the Sanctus, and the prostrations of various prophets before the presence of God are recalled in the prostration of the priests before the bishop on the day of their ordination. But the way biblical examples inform, inspire and give symbolic meaning to the Church's liturgical actions is entirely different from the approach of lifting liturgical practices directly from the Scriptures, as Protestants and some Catholics of the charismatic persuasion tend to do. So, to go back to our original example, the fact that Moses went barefoot before God during a theophany does not translate into a general liturgical directive.
What about the Saints?
One could possibly try to save the argument in favor of going about barefoot before the Blessed Sacrament by invoking the example of certain poor saints who went about barefoot continually as an expression of their vow of poverty. St. Francis, for example, went about barefoot constantly, and we have no evidence from his various biographies that he ever made an exception for going to Mass. Thus, he probably attended Mass barefoot. If St. Francis attended Mass barefoot as an expression of his consecration to God, and if we can presume his consecration was pleasing to God, then does this not provide us with a precedent for doing likewise?
I certainly do not deny that we ought to imitate the saints; but on the other hand, we must acknowledge that an action that is proper so someone in one state in life may not be proper for someone in another state in life. For example, a religious attends Mass clothed in the habit of their order. In the case of the Franciscans, this is a long brown habit. This is (or should be) normal, and we should not be surprised by it. But, suppose a lay person who is in no way affiliated with the Franciscans were to decide that they, too, wanted to attend Mass wearing a long, brown robe. I think we can understand that this would be something totally different, even if the outfit of the lay person looked exactly the same as the Franciscan habit; even if the lay person had actually borrowed a legitimate Franciscan habit, it would not be acceptable for them to wear it, because they are not a Franciscan, and wearing a habit does not make one a Franciscan. The lay person would simply be wearing a costume to Mass, something that is inappropriate.
So, the fact that St. Francis may have come to Mass barefoot does not give lay people precedent to do so as well. The bare feet of St. Francis were an expression of his radical devotion to poverty and his absolute consecration to God; as such, they were part of his "habit" just as much as his brown patchwork robe. Can lay people who want to go around the sanctuary barefoot make the same claim? Only with the greatest disingenuity.
The Crux of the Matter
The crux of the matter is that matters of liturgy have their own principles and decorum that are internal to the development of the liturgy in the Roman rite down through the centuries. It is to these principles, interpreted and enforced by the Magisterium (or the bishops as delegated by the Magisterium) that we must look for the proper manner of understanding what is and is not appropriate behavior in the Mass and in the sanctuary. We cannot simply lift things from the Bible or from the lives of the saints and translate them into the liturgy, especially when the original behaviors were not done in a liturgical context. The history of the Roman rite and the norms developed within that specific tradition are the only valid interpretive guidelines for what is and is not acceptable in the Latin rite liturgy. No matter how well intentioned we may be, simply lifting episodes out of the Bible, cutting and pasting stories from saints lives, or incorporating extra-liturgical cultural expressions into our liturgy (like hand-shaking) do not contribute to a proper, reverent liturgy. They inevitably serve as forces driving the liturgy to become something other than it is, something man-made, centered on emotions rather than worship of God.
Coming to Mass barefoot and going about the sanctuary with no shoes on cannot but create an atmosphere of undue casualness, a casualness that neither the saints nor the prophets of the Old Testament nor the Apostles ever had in the authentic presence of God. It is always a practice to be deplored, and becomes even more scandalous when certain priests and youth directors actively encourage the practice as a means of acting out the errant sort of spirituality critiqued above.
Put your shoes back on. Please.