A Sacramental of the Church.
The word "vestment" is from the Latin, and signifies simply clothing, but it is now used generally to denote the garments worn by the ministers of religion in the performance of their sacred duties.
Vestments are a sacramental -- that is, they are set apart and blessed by the Church to excite good thoughts and to increase devotion in those who see and those who use them. They are the uniform of the priest when he is "on duty," while he is exercising the functions of his ministry and using the sacred powers which he received at his ordination.
Colors of the Vestments.
The Church ordinarily permits the use of [four] colors in the sacred vestments -- white, red, green, [and] violet... Gold may be used as a substitute for white, red or green.
Each of these colors has its own meaning. The Sacrifice of the Mass is offered for many purposes and in honor of many classes of saints; and these various purposes are all designated and symbolized by the color of the vestments which the Church prescribes for each Mass.
When are these colors used? When the Church wishes to denote purity, innocence or glory, she uses white; that is, on the feasts of our Lord and of the Blessed Virgin, on the festivals of angels and of all saints who were not martyrs. Red is the color of fire and of blood; it is used in Masses of the Holy Ghost, such as on Pentecost, to remind us of the tongues of fire -- and on the feasts of all saints who shed their blood for their faith. The purple or violet is expressive of penance; it is used during Lent and Advent (except on saints' days), and also on the sorrowful festival of the Holy Innocents. [White] is the color of [the resurrection and so is used in masses] for the dead. Red is used on Good Friday and Palm Sunday. Green is the color which denotes the growth and increase of our holy Church, and is also symbolic of hope; it is used at various times of the year, on days that are not saints' days.
A Priest's Vestments.[1562 "The function of the bishops' ministry was handed over in a subordinate degree to priests so that they might be appointed in the order of the priesthood and be co- workers of the episcopal order for the proper fulfillment of the apostolic mission that had been entrusted to it by Christ." Catechism of the Catholic Church.]
The black gown of the priest, called a cassock or soutane, is not a vestment. It is simply the ordinary outer garb [of a priest used frequently in the past. The Columbia Encyclopedia states: "The cassock, a close-fitting gown buttoning down the front and reaching to the feet, is not a vestment so much as the daily uniform of the Western priest."
"[In the past Clergy] must wear a costume suited to their state. While the common canon law does not determine in every detail what the dress of clerics should be, yet many and various prescriptions on the subject are found in the canons, the pontifical constitutions, and the decrees of councils. These ordain that the clerics are not to wear the dress of laymen. They must abstain from gaudy colours, unbecoming their state. The wearing of the soutane or cassock on all occasions, even in public, is prescribed forclerics living in Rome, and bishops may command the same in their dioceses. In non-Catholic countries, synods generally prescribe that for public use the dress of clerics should be such as to distinguish them from laymen; that is of black or of a sober colour, and that the so-called Roman collar be worn." Catholic Encyclopedia, 1913.
Today a priest might be seen in regular "street clothing", or in a shirt with a Roman collar, and in a more formal setting a suit with a clerical shirt. The color is usually black. This is his normal working uniform when he is not officiating at a liturgy or performing a sacrament.]
The vestments worn by the priest at Mass are as follows: the alb, the cincture, the stole, and the chasuble; and at certain other services he may use the cope, the humeral veil and the surplice. Each of these has its own history and its own symbolical meaning...
The Alb. The long linen gown worn by the priest is called the alb, meaning simply the white garment... It is a survival of the white Roman toga. Its white color denotes the necessity of purity, both of soul and body, in him who offers the Lam of God to the Father.
The Cincture. This is the proper name for the girdle worn around the waist to bind the alb closely to the body. In some countries it is of the same color as the vestments used, but among us it is generally white. It is made of braided linen, or sometimes of wool... [Exod. 29:9 "and you shall gird [Aaron and his sons] with sashes and tie headdresses on them; and the priesthood shall be theirs by a perpetual ordinance." NRSV]
The Stole. At Mass, and also in nearly every other religious function, the priest wears around his neck a long narrow vestment, the ends hanging down in front. The deacon📷 at ... Mass wears a similar vestment, but in a different manner -- diagonally from his left shoulder to his right side. The stole came into use about the fourth century, and was originally a sort of robe or cloak; but its form was gradually modified until it became a narrow strip. It is said by some to have been the court uniform of Roman judges, and to have been adopted by the Church to denote the authority of her ministers..
The Chasuble. The most conspicuous part of the costume of the priest at Mass is the chasuble, the large vestment worn on the shoulders and hanging down in front and behind. The rear portion is often, though not always, ornamented with a large cross.
The word chasuble is from the late Latin "casula," a little house, because it is, as it were, a shelter for the priest...
This vestment has been greatly altered during the centuries of its history. It was originally a large mantle or cloak, with an opening for the head in the center, and had to be raised at the sides to allow the hands to be extended outside the cloak. The assistants at the Mass were obliged to help the priest by holding up the sides of the chasuble...[due to its size and weight if heavily ornamented].
The Cope and Veil. The cope... was originally worn only in outdoor processions, and was considered merely as a rain-cloak, as is shown by its Latin name, pluviale, a protection against rain. The cape attached to it, which now has no use whatever, is a reminder of the large hood formerly used to cover the head in stormy weather. Our English name, cope, is from the Latin "cappa," a cape.
The humeral veil was worn on the shoulders of the priest at the Benediction of the Blessed Sacrament when he held the Sacred Host for the blessing of the people, and also when he carried the Blessed Sacrament in procession.
The Surplice. It may be well also to say a word about this vestment, which is worn over the cassock at the administration of the Sacraments and at various services of the Church. It is the special garb of clerics not in sacred orders, and its use is tolerated for lay altar-boys, or acolytes, in our churches.
In its present form it is one of the most modern of vestments. The word surplice is from the Latin "superpellicium" -- a dress worn over furs. In the Middle Ages it was allowed to the monks in cold countries to have fur garments, and over these a linen gown was Surplice worn in choir. It was later considered practically as an alb, and in the twelfth century it was usually so long that it reached the feet. Gradually it was made shorter, and about the seventeenth century the custom began of ornamenting it with lace.
The Tunic and the Dalmatic. The tunic is the vestment of subdeacons (ordination to the subdeaconite was discontinued after Vatican II), the dalmatic of deacons. They are usually exactly alike, although, strictly speaking, the tunic should be of smaller size than the dalmatic. Each is of about the same length as the chasuble of the priest. These vestments hang from the shoulders, which are covered by projecting flaps; these are sometimes connected under the arms, so as to resemble short sleeves. The color, of course, varies according to the Mass, and on the back are usually two ornamental vertical stripes, but no cross. [A deacon will now often appear in just alb and stole.]
A tunic signifies simply an outer garment. The dalmatic gets its name from a Roman garment made of wool from the province of Dalmatia, worn under the outer clothing in ancient times...