Is

My very useful guidebook on all things liturgical, Bread of Life, Cup of Salvation, by John Baldovin, S.J., which I highly recommend, has very little say about the actual Lamb of God prayer. He makes just one comment about it, but it's a good one: "This chant," he says, "with its 'you take away the sins of the world,' is another reminder that in our participation in the Mass Christ is uniting us to the work of salvation." That is to say, the prayer reminds us of what Jesus does -- he takes away the sins of the world -- and asks him to include us in that ongoing work.

Personally, I think I'd push it even further and say that this little prayer is the moment in which we acknowledge that the merciful presence of Jesus which we've been praying for is in fact present in the eucharist which we will receive, and we ask for that mercy to be effective -- that is, to forgive and reconcile us. So afterwards the presider's words make sense: This is the Lamb of God, who takes away the sins of the world. Happy are we who are called to this supper. We are happy because Christ is present among us. (That one little word, "is" -- it packs quite a punch.)

Not too long ago in the Church people were taught to be fearful of going to communion if they hadn't first confessed all of their sins. But as we've continued to study the sacrament, we've also come to rediscover that communion is itself the ongoing sacrament of reconciliation. That is, it, too, is a means by which Jesus reconciles us to one another and to himself.

And so at this moment, before we receive communion, we ask that it might work, that we might be drawn up into Christ's mercy, forgiven and healed.

Guercino's Return of the Prodigal Son