28 • After this, Jesus,
knowing that all was now finished,
said (to fulfill the Scripture), "I thirst."
29 • A jar full of sour wine stood there,
so they put a sponge full of the sour wine on a hyssop branch
and held it to his mouth.
30 • When Jesus had received the sour wine,
he said, "It is finished,"
Two sayings of Jesus from the cross stand very close together here and John, the only gospel to mention either, gives us the details of the one within the recounting of the other. It makes perfect sense if the 'I thirst.' saying is excluded:
Jesus,knowing that all was now finished,… said, "It is finished,"so we ought to pick up on the 'I thirst' episode as having something to do with being finished.
The sour wine wasn't intended as a punishment and we're not told about it so that we might feel additional pangs of sorrow on Christ's behalf. Just because the wine was sour meant that its acidity was immediately detectable even to the most preoccupied palate. There is a clear contrast between Jesus just tasting and refusing to drink before and his taking time to drink after it was finished.
What was it that was finished? Strangely enough, since this is before his actual death, it was nevertheless the dying that was finished with. None of this sequence of events makes sense unless we take it at face value that Jesus was dying on the cross in order to put right what was wrong and it follows that what was finished was the work of putting right.