A.T. Robertson Commentary John 19:28

"After this Jesus, knowing that all things are now finished, that the scripture might be accomplished, saith, I thirst." — John 19:28 (ASV)

Are now finished (ηδη τετελεστα). Perfect passive indicative of τελεω. See same form in verse 30. As in 13:1, where Jesus is fully conscious (knowing, ειδως) of the meaning of his atoning death.

Might be accomplished (τελειωθη). First aorist passive subjunctive of τελειοω rather than the usual πληρωθη (verse 24) with ινα. John sees the thirst of Jesus in Ps 69:21f. Jesus, of course, did not make the outcry in any mechanical way. Thirst is one of the severest agonies of crucifixion. For the "perfecting" of the Messiah by physical suffering see Heb 2:10; 5:7f..