Why this dress code?
What is of concern is not only whether the clothing worn by those in attendance is modest, but if it is appropriate as well. For, it is no less than the court of Heaven and the Throne of God Himself to which the faithful present themselves when they enter through the door of the chapel, and especially when they kneel before the altar to receive the Body, Blood, Soul, and Divinity of Jesus Christ.
Immodest and blatantly casual dress in the church is not only an insult to God but a scandal to fellow Catholics, particularly those who are young and impressionable.
While deliberate immodesty by revealing dress is always sinful, modest but inappropriately casual dress in church is outwardly disrespectful to God and causes the offender and all those whom he or she influences to forget where they are, which leads to complacency and irreverence before the Blessed Sacrament, the loss of faith, and ultimately, the forfeiture of the Sacraments.
For an example of this phenomenon, we need only recall that the conciliar church relaxed its dress code in the 1960s, which was followed by a decline in belief in the Real Presence among its members, and culminated with the loss of the Real Presence itself before the end of the decade.
If we expect God’s blessing, protection, and preservation of our oasis of true Catholic worship to continue until that hour when the ecclesiastic, cultural, and moral crisis is finally brought to an end, we must merit that great favor by faith, good works, and by presenting ourselves in a respectful manner before Almighty God in His holy temple.