5 Nor need we be disturbed with the question, how the sponge could be applied to His mouth when He was lifted up from the earth on the cross. For as we read in the other evangelists, what is omitted by this one, it was fixed on a reed, so that such drink as was contained in the sponge might be raised to the highest part of the cross. By the reed, however, the scripture was signified, which was fulfilled by this very act. For as a tongue is called either Greek or Latin, or any other, significant of the sound, which is uttered by the tongue; so the reed may give its name to the letter which is written with a reed. We most usually, however, call those tongues that express the sounds of the human voice: while in calling scripture a reed, the very rareness of the thing only enhances the mystical nature of that which it symbolizes. A wicked people did such things, a compassionate Christ suffered them. They who did them, knew not what they did; but He who suffered, not only knew what was done, and why it was so, but also wrought what was good through those who were doing what was evil.
6. “When Jesus therefore had received the vinegar, He said, It is finished.” What, but all that prophecy had foretold so long before? And then, because nothing now remained that still required to be done before He died, as if He, who had power to lay down His life and to take it up again, had at length completed all for whose completion He was waiting, “He bowed His head, and gave up the ghost.” Who can thus sleep when he pleases, as Jesus died when He pleased? Who is there that thus puts off his garment when he pleases, as He put off His flesh at His pleasure? Who is there that thus departs when he pleases, as He departed this life at His pleasure? How great the power, to be hoped for or dreaded, that must be His as judge, if such was the power He exhibited as a dying man!
Source: Tractates on the Gospel of John (New Advent)