The altar receives its importance in connection with the Holy Sacrifice of the Mass that is celebrated upon it. It has been set apart for this purpose and the bishop consecrates it when it is installed in a new church. The ceremony of consecration mimics in some ways the baptism of a new Christian as the bishop uses holy oils to bless the altar and vests it with a white garment after the prayers have been completed. Kissing the altar can then be viewed as honoring the special role it has in the liturgy and the consecration it was given by the bishop.

Symbolically the altar is often said to represent Jesus Christ, the “cornerstone” of the Church (cf. Ephesians 2:20). During the history of the liturgy the priest would sometimes kiss the altar before blessing the people, symbolizing how the blessing came from God, not the priest. Additionally, over time relics of saints were inserted into the altar and when the priest kissed the altar, he would be kissing the relics as well.

So while it is true that altars are material objects, they have been set apart for a specific purpose and kissing the altar recognizes its privileged role and relation to the divine sacrifice of Jesus Christ. (Philip Kosloski – July 26, 2017)