These "drink offerings" of sour wine and gall perfectly fulfilled David's prophecy of Psalm 69:21: "They also gave me gall for my food, and for my thirst they gave me vinegar to drink."
But what was this "sour wine"? Easton's Bible Dictionary describes this drink in its article, "Gall":
The drink offered to our Lord was vinegar (made of light wine rendered acid, the common drink of Roman soldiers) "mingled with gall," or, according to Mark 15:23, "mingled with myrrh"; both expressions meaning the same thing, namely, that the vinegar was made bitter by the infusion of wormwood or some other bitter substance, usually given, according to a merciful custom, as an anodyne [pain reliever] to those who were crucified, to render them insensible to pain. Our Lord, knowing this, refuses to drink it. He would take nothing to cloud his faculties or blunt the pain of dying. He chooses to suffer every element of woe in the bitter cup of agony given him by the Father (John 18:11).
Other commentators opine that the gall—being a poison as well as a desensitizing drug—was meant to speed the death of the victim before the grisly effects of the crucifixion did. But surely it was not offered as, Easton suggests, for the comfort of the condemned! Rather, it was given for the soldiers' own ease and perhaps for the benefit of the pitiless Jewish leaders who wanted the three victims dead and disposed of before the beginning of the Feast of Unleavened Bread (John 19:31-33).
Luke's account implies that the soldiers' offers of sour wine to Jesus were part of their mockery of Him: "The soldiers also mocked Him, coming and offering Him sour wine" (Luke 23:36). It is not logical that these soldiers would mock Jesus, beat Him, spit on Him, jam a crown of thorns on His head, flog Him terribly, and then give a pain-relieving drink to Him as a "merciful custom"! Later, to speed their deaths, the soldiers would break the legs of the two men who were crucified on either side of Jesus and would cruelly stab Him with a spear. They would have broken Jesus' legs too, but they were prevented from doing so for the prophecies to be accurately fulfilled. Not much evidence of mercy here!
Of Sponges and Spears