Behold the Lamb of God, behold him who takes away the sins of the world. Blessed are those called to the supper of the Lamb. (Order of Mass, Roman Missal, 3rd ed.)
These are the words we hear at every Mass, just before we receive Holy Communion, as the priest elevates the Host and invites us to behold the Lord. He calls us to the supper of the Lamb. Images of a meal, a supper come to mind, especially the Last Supper. However, this verse is from Sacred Scripture and its context is quite meaningful.
6 Then I heard what seemed to be the voice of a great multitude, like the sound of many waters and like the sound of mighty thunderpeals, crying, "Hallelujah! For the Lord our God the Almighty reigns. 7 Let us rejoice and exult and give him the glory, for the marriage of the Lamb has come, and his Bride has made herself ready; 8 it was granted her to be clothed with fine linen, bright and pure"-- for the fine linen is the righteous deeds of the saints. 9 And the angel said to me, "Write this: Blessed are those who are invited to the marriage supper of the Lamb." (Rev 19:6-9)
Our supper of the Lamb is really the marriage supper of the Lamb. He is the groom, and we are the bride. As has been often described in this blog, Sacred Scripture frequently symbolizes God as male, especially as a groom; likewise Scripture symbolizes the Church (us) as female, especially as a bride. We and God come together in a covenant bond, similar to that of a bride and groom in marriage. The result is a conjugal love, bearing fruit in a newness of our soul.
Side note: Once upon a time, all Catholic women 'covered their heads' during the liturgy. What they actually did was wear a veil, imaging a bridal veil - this was a symbol adding clarity to the Mass, that what was happening was a wedding feast between God and His bride.
In our text above, note v. 7 says the "Bride has made herself ready" by clothing herself in "the righteous deeds of the saints." As a bride adorns herself with beautiful clothing, so we adorn ourselves in the Liturgy with the holiness of the saints, all saints in all times. We participate in their actions, their lives. This liturgical feast is a gathering of the whole Church - those on earth, those in heaven, and those in Purgatory. The Mystical Body of Christ comes together in every Mass, because we are united, in communion with each other through the central hub of Jesus, our head. Hence, we call this sacrament Holy Communion.
Perhaps in all this talk of a marriage supper, we focus on the Mass as a shared meal among the communion of saints. It is a correct undertanding. But our text subtly reminds us of another element in the Eucharist, which is critcial: the groom is a Lamb. We know from The Old Testament that a lamb is the creature of sacrifice. Our God sacrificed Himself for the redemption of sins. As of old, the covenant was sworn by a sacrifice, which was slaughtered and eaten. Those who ate swore the covenant with each other. Such covenant sacrifices had two elements: lambs were slaughtered, and they were eaten. So our Eucharist has both of these elements. So our Roman Missal commands us immediately before Holy Communion to look upon the sacrifical Lamb, sacrificed to take away the sins of the world. It reminds us of the sacrifical nature of the Eucharist, just before we enjoy the marriage feast of the Lamb, our beloved groom.