Liturgical dress is not decoration and it is not a uniform. It is a notation. Every major vestment carries a restriction, and the restrictions together let anyone who can read them identify, from the back of a church, who is present and what office each person holds.
The grammar is consistent enough to set out plainly.
- Alb. No restriction at all. Bishop, priest, deacon, server and lay reader wear the same white tunic, and it is tied to baptism, which everyone has. It is the deliberate exception, and it goes on first.
- Stole. Ordination, and nothing else. No unordained person wears one. Worn hanging straight from both shoulders by a bishop or priest; worn across the body from left shoulder to right hip by a deacon. That single difference distinguishes the two orders at a glance and is the most useful thing to know.
- Dalmatic. The deacon's outer vestment, and his alone.
- Chasuble. The priest or bishop celebrating the Eucharist, and only while celebrating. A priest in the congregation at somebody else's Mass does not wear one.
- Cope. Everything except the Eucharist, processions, Benediction, solemn Evensong, weddings and funerals without a Mass. Less restricted, and in cathedrals worn by many at once.
- Mitre. Bishops, and abbots. It goes on and comes off during the liturgy according to what the bishop is doing: off when praying to God with the church, on when teaching or blessing it. The headgear itself encodes the difference between the two.
- Pallium. A narrow woollen band, restricted to the pope and to metropolitan archbishops, conferred individually. The narrowest restriction in the system.
Colour runs across all of it and marks the calendar rather than the person: white at Christmas and Easter, red at Pentecost and for martyrs, green through ordinary time, violet in Advent and Lent, black or violet for the dead.
So a congregation looking at the sanctuary is reading two things at once, who these people are, and where the church is in its year. The system was not designed as a code and grew by accretion out of late Roman clothing, but it functions as one, and the fact that it can be read is why arguments about vestments have never been merely aesthetic.