The long black garment which the priest wears around the church in all the sacred functions is called a cassock. Kings and officers of the army wear a special uniform when performing their public duties; priests wear cassocks and other special garments when performing their public duties. These vestments are used to excite the minds of the faithful to the contemplation of heavenly things.
Who, for example, can behold the cross on the chasuble the priest wears without thinking of all Christ suffered for us on the cross? As the priest in celebrating Mass represents the person of Christ, and the Mass represents His passion, the vestments he wears represent those with which Christ was clothed at the time of the passion.
The first vestment the priest puts on over the cassock is called an amice. It is made of linen, and reminds us of the veil that covered the face of Jesus when His persecutors struck Him. (Luke xxii. 64.)
When the priest puts on the amice he first places it on his head, thus recalling to mind the crown of thorns that pierced the head of Jesus.
The alb (from albus, white) represents the white garment with which Christ was vested by Herod when sent back to Pilate dressed as a fool. (Luke xxii. 11.)
White is emblematic of purity. Hence the wearer is reminded of that purity of mind and body which he should have who serves the altar of the Most High.
The cincture, or girdle, as well as the maniple and stole, represent the cords and bands with which Christ was bound in the different stages of His passion. St. Matthew says in the 22d verse of the 27th chapter, "They brought Him bound and delivered Him to Pontius Pilate, the governor."
The chasuble, or outer vestment the priest wears, represents the purple garment with which Christ was clothed as a mock king. "And they clothed Him with purple" (Mark xv. 17). Upon the back of the chasuble you see a cross. This represents the cross Christ bore on His sacred shoulders to Calvary, and upon which He was crucified.
In these vestments, that is, in the chasuble, stole, and maniple, the Church uses five colors—white, red, purple, green, and black.
White, which is symbolic of purity and innocence, is used on the feasts of Our Lord, of the Blessed Virgin, of the angels, and of the saints that were not martyrs.