Church vestments derive from ordinary clothing in apostolic times. “Fashions” changed very little overall in the first 5 centuries of Christianity. People in ancient times wore “Sunday best” for Church. Since these garments got very little wear, and were highly prized, they did not quickly wear out. So, while street fashion gradually evolved, Church fashion remained more stable.
Historians of costume call this sort of carry-over “fossil” costume. The folk dress of Europe and Scotland, as worn today, is “fossil” fashion. A similar phenomenon is the white tie and tails or striped trousers and cutaway coats now worn at formal occasions. These styles originated in the 19th Century and remain pretty much the same today.
At the Masses for the Pope, you saw cardinals dressed in big circular garments like ponchos. These are called chasubles and originated in Roman times as cloaks (a similar garment called a cope, which is open down the front, is worn for other ceremonies in the Church).
Over time these garments became “color coded” so that white (or gold), green, red, and violet each symbolizes a particular theme (joy, martyrdom, the Holy Spirit, penitence) and is designated for particuilar liturgical seasons or occasions.
The white garment, which looks like a long-sleeved nightgown, and is worn underneath the chasuble, was the universal basic undergarment in the ancient world up to about the 15th Century.
The “hat” is not so ancient. It is called a mitre (or miter) and apparently dates from around the year 1000. It is worn only by bishops (except for a couple of distinct exceptions) and is said to symbolize the flames of the Holy Spirit descending upon the Church at Pentecost.
I am not sure I understand how your statement that Jesus went about as a humble man relates to this. For starters, the seamless garment for which the Roman soldiers cast lots at the foot of the cross, was quite valuable, and a remarkable achievement of the weaver’s art.
Beautiful vestments and ornaments of worship are, for Catholics, parallel to the “pound of costly ointment” with which Mary anointed the feet of Jesus in Jn 12:3). Only Judas objected to that.
