An interesting question came up in our house chapter (i.e. community meeting) last night: does it matter what we wear for Mass and Liturgy of the Hours? My province of the Order is pretty casual on this point; there is no expectation that a brother would wear his habit to chapel when we pray in the house. Most would put it on for liturgies in public, though not all.
We were questioning ourselves on this point. Does the relative neatness and formality of someone's external appearance reflect his internal spiritual condition? It's not an easy question, and the answer is both yes and no.
Soul and body are distinct, but in a deep and mysterious relationship. Together they constitute the person who has a vocation in this world and an eternal destiny in the next. We believe in the bodily resurrection, and though it might be difficult to articulate exactly what this might mean, we know that the whole person will go into eternity. As one of my favorite teachers liked to say, "eschatologically speaking, the human being is not a two-stage rocket."
Thus, the exterior does have significance for the interior, and vice versa. When we desire to express our reverence for sacred spaces and times, a neatness or formality in our external appearance is a natural and obvious means. With our more serious and formal clothes on, we then behave in a more serious and reverent manner.
When I first began attending a Mass in the Extraordinary Form, one of the things that immediately edified me was the care the people seemed to have taken with their dress and appearance. As I have written about many times, what hooked me into an interest in the EF was the discovery of a reverence and recollection among the people that I had been missing in some other parts of my liturgical life. No doubt the practice of dressing in a particular or formal way for Mass was formative for them as well.
On the other hand, I think that care must always be taken not to push such reflections and claims too far. I suspect that some of the most sincere prayers in this world come from people who both feel and look a mess. Some religious will say that the relative neatness and cleanliness of one's room or appearance is indicative of the state of soul and vocation within, but this is not always the case. Along the way I have met very spiritual brothers who were quite slovenly and even dirty. On the other hand, sometimes someone will try to deal with internal chaos by controlling the neatness of his external world.