The sermon opens with a bleak diagnosis: the world is sick with sin, incurable, fallen into chaos and disorder, and everyone outside of Christ is groping in darkness, without hope and without God, under His wrath. Into that darkness comes God’s provision: John the Baptist points to Jesus and says, “Behold, the Lamb of God who takes away the sin of the world.”
At the cross, a substitution takes place — Christ, who knew no sin, became sin for us, bearing what we deserved so that we might become the righteousness of God in Him. That work does not end at the cross: the coming of the Holy Spirit at Pentecost begins the new creation, so that anyone in Christ is already a new creature, with the old life gone and a new one begun.