According to the General Instruction of the Roman Missal 296, “The altar on which the Sacrifice of the Cross is made present under sacramental signs is also the table of the Lord to which the People of God is called together to participate in the Mass, as well as the center of the thanksgiving that is accomplished through the Eucharist.”
The Christian altar is one of the earliest elements of the liturgy. In the first years when Christianity was illegal, the Eucharist was typically celebrated in the homes of the faithful. The altar could have been the dinner table in the home or the wooden chest in which a bishop would carry needed materials for celebrating the Eucharist from place to place.
The earliest stone altars were the tombs of the martyrs interred in the Roman Catacombs. The practice of celebrating Mass on the tombs of martyrs can be traced with a large degree of probability to the first quarter of the second century.
The altar is the table on which the Eucharistic Sacrifice is offered. Mass may sometimes be celebrated outside a sacred place, but never without an altar. The altar is consecrated by the bishop before it is used.
The altar is the focus of our attention during the celebration of the Mass. (9:40)