The altar is the sacred table on which Mass is offered. Before Mass may be celebrated on it, it must first be consecrated by the Bishop.
The right and left sides of the altar are so called from the
right and left hands of the crucifix so that the right side is the Gospel side and the left side is the Epistle side. Up to the fifteenth century it used to be just the opposite according to the right and left hand of the priest.
It is of strict obligation that every altar upon which the Holy Sacrifice is offered should be covered with three linen cloths. Before these cloths are used they must be blessed by the Bishop or by one of his delegates.
Three altar cloths are used in honor of the Blessed Trinity, as well as to commemorate the linen cloths in which Our Lord's Body was wrapped in the sepulchre.
Relics of Saints are placed in the altar because in the time of persecution it was customary to say Mass on the tombs of the Martyrs. When peace was restored to the Church this custom gradually gave way to that of laying in the newly consecrated altars some portion of the Martyrs' bodies.
53. Who places the relics of the Martyrs in the altar? The Bishop, who consecrates the altar, places the relics in it.
54. What must be on the altar whenever Mass is said?
There must be, besides the three altar cloths, a crucifix and two lighted candles and usually a Missal. Missal-stand and three altar cards.