"...he sees Jesus coming toward him, and says, 'Behold, the Lamb of God, who takes away the sin of the world!'" (John 1:29).
The above is how this verse reads in the original Greek. The verbs are present tense because Jesus comes to us now, in the present.
It's as though John the Baptist is speaking to us, and we are the disciples who hear his words and follow Jesus (vs. 37).
But then change the "he" to "we," and you get the perfect description of the Divine Service (the worship service as practiced by Lutherans and others). How so?
The pastor speaks (or sings) the Words of Institution over the bread and wine and then shows them to the people. The congregation, in faith both simple and profound, believes that they are beholding not only bread and wine but the body and blood of Jesus. He is coming toward them, as it were, and soon they will receive Him into themselves. And what do they do? They sing "Lamb of God" (Agnus Dei in Latin):
Lamb of God, You take away the sin of the world; have mercy on us.
Lamb of God, You take away the sin of the world; have mercy on us.
Lamb of God, You take away the sin of the world; grant us peace.
We are disciples of Jesus, the crucified and risen. But it is John who teaches us what to say and sing when we see Him coming toward us in Holy Communion: Agnus Dei (Lamb of God).
