Not only is the altar a sign of Christ and a locus for the Paschal meal, but the altar is, in a very real way, a memorial for martyrs to the faith. Read this section:
5. All the dignity of the altar rests on its being the Lord’s table. Thus the martyr’s body does not bring honor to the altar; rather the altar does honor to the martyr’s tomb. For it is altogether proper to erect altars over the burial place of martyrs and other saints or to deposit their relics beneath altars as a mark of respect and as a symbol of the truth that the sacrifice of the members has its source in the sacrifice of the Head.(cf. Common of Martyrs 8, prayer over the gifts) Thus ‘the triumphant victims come to their rest in the place where Christ is victim: he, however, who suffered for all, is on the altar; they who have been redeemed by his sufferings are beneath the altar.’(Ambrose, Epistula 22, 13: PL 16, 1023. See Ps. Maximus of Turin, Sermo 78: PL 57, 689-690.) This arrangement would seem to recall in a certain manner the spiritual vision of the Apostle John in the Book of Revelation: ‘I saw underneath the altar the souls of all the people who have been killed on account of the word of God, for witnessing to it.’(Rev 6:9) His meaning is that although all the saints are rightly called Christ’s witnesses, the witness of blood has a special significance that only the relics of the martyrs beneath the altar express in its entirety.
Probably a good homiletic point for the dedicaiton Mass, if relics are to be housed in or under the altar. This is perhaps a bit more graphic than the churchy sensibilities of some might want to encounter. but it is a very real part of the faith, and need not be minimized.