This shows how ignorant you are. Liturgy IS the reason! The sacraments are the reason.
Also, what ‘finery’? What ‘gold’? Most priests wear ready-made polyester chasubles purchased at a religious supply store for less than $200.
If you mean the pope, he does not wear ‘gold’ or precious jewels except for his ring, and this pope’s is plain silver.
Your “curious” questions are so full of wrong assumptions it’s impossible to give you an answer in this format. This has a history of 2000 years, look into it with some respect, please.
I see what they wear during some high Mass or something. And it’s not just the Catholic church but other denominations. Normally you are right, they wear a cassock of some sort. And the reason I asked questions here I thought that maybe perhaps I could get some answers without all the nasty replies. Guess I was wrong. Salvation however provided me with links that can. Thanks anyway and enjoy life.