The NRSV translation of the Bible put John 19:28-29 in this way: "After this, when Jesus knew that all was now finished, he said (in order to fulfil the scripture), ‘I am thirsty.’ A jar full of sour wine was standing there. So they put a sponge full of the wine on a branch of hyssop and held it to his mouth."
Some talk about the scripture that is being fulfilled is Psalm 69:21 - "They gave me poison for food, and for my thirst they gave me vinegar to drink." Meaning the fulfilment comes in the type of drink that was given to Jesus.
I guess. But does the drink type serve as a convincing argument for Jesus as Messiah? And, in his final moments, I question that Jesus is thinking, "Oh, hey I could fulfill an obscure scripture about drinking vinegar if I just request a drink. I know, I will say 'I thirst.' That will do it."
Perhaps it is a misunderstanding to interpret "I am thirsty" as fulfilling one verse of of the scriptures. Perhaps in this line, Jesus fulfils all of scripture?
Throughout the biblical witness, there is a revealing story about the nature of God. That is God is a God who is constantly pouring God's self out out of love for creation. This is made most evident in the life of Jesus who identified himself as the source of the water of life (John 4). But even after death, when Jesus' side is pierced and water and blood flow out, God continues to be poured out onto creation.
Could it be that Jesus is thirsty because he has poured himself out so much out of love for creation that he himself grows thirsty? He gives the water of life to others to the point that he goes thirsty. Could it be that God goes without the waters of life so that others may have their thirst quenched?
On a smaller scale, Christians fast for similar reasons. We do not eat so that others may. And so when we give away our food so others may be fed, we become hungry. When God gives the waters of life away so creation may drink, God becomes thirsty.
The thirst of God in Jesus is also a bit different from the thirst of other gods of the day. Other god's have a thirst that cannot be quenched. They have an thirst that demands that creation offers up sacrifice after sacrifice in order to quench their thirst. These gods are thirsty for more. God in Christ is not thirsty for more, but thirsty because he gave all that he has.