This is the first hymn in a new section: "Passions-Lieder oder Lieder vom Leiden und Sterben Jesu Christi." "Passion Songs or Songs of the Suffering and Death of Jesus Christ."
Christe, du Lamm Gottes,der du trägst die Sünd der Welt,erbarm dich unser!Christe, du Lamm Gottes,der du trägst die Sünd der Welt,erbarm dich unser!Christe, du Lamm Gottes,der du trägst die Sünd der Welt,gib uns dein Frieden! Amen.Spangenbergs Kirchengesangbuch, 1545.
My prose translation:
Christ, You Lamb of God,You Who carry the sin of the world,Have mercy on us!Christ, You Lamb of God,You Who carry the sin of the world,Have mercy on us!Christ, You Lamb of God,You Who carry the sin of the world,Give us Your peace! Amen.Spangenberg's Church Songbook, 1545.
Most of this text comes straight from John 1:29 where John the Baptist says, "Behold, the Lamb of God, who takes away the sin of the world!" The line "Give us Your peace" may refer to the first part of John 14:27 where Jesus says, "Peace I leave with you; my peace I give to you."
This hymn appears as "O Christ, Thou Lamb of God" in The Lutheran Hymnal (#147). It also appears in Lutheran Worship (p. 151, 172, 191) and in The Lutheran Service Book (p. 163, 180, 198), but in those hymnals, it's part of the liturgy. The Gesangbuch notes that the text is sung to "its own melody," which is how it appears in TLH. LW and LSB each have multiple different melodies for the text, but the one that corresponds to TLH #147 is on page 151 in LW and on page 198 in LSB.