17 • And he took a cup,
and when he had given thanks
he said, "Take this, and divide it among yourselves.
18 • For I tell you that
from now on I will not drink of the fruit of the vine
until the kingdom of God comes."
19 • And he took bread,
and when he had given thanks, he broke it
Before the taking of the bread that is 'his body', before the taking of the cup that is 'the new covenant in Christ's blood,' that is, during the Passover seder but before Jesus took up those elements of the seder that he instituted as the sacrament of the Lord's Supper, he took a cup of wine and told the disciples to share it among themselves. Why'd he do that?
What he was saying about the coming of the kingdom of God is entirely consistent with what he had been saying about the Passover being fulfilled in the kingdom of God. The big question that the disciples must have had was when the kingdom of God could be said to have come but now they had an answer. The kingdom of God would have come when Jesus once again drank wine.
What Jesus was doing is significant. Up till this moment he had been with the disciples but the moment was coming when he was to be separated from them. This sharing out of the cup and the declaration of not drinking wine again until the coming of the kingdom of God is a vow of separation. There was a set way of making such a vow laid down in the Torah and the disciples could not have missed the connection. The two seals of this vow were not getting one's hair cut during the time the vow was in operation and not drinking wine during that time. The instructions about the wine are very thorough:
he shall separate himself from wine and strong drink. He shall drink no vinegar made from wine or strong drink and shall not drink any juice of grapes or eat grapes, fresh or dried. All the days of his separation he shall eat nothing that is produced by the grapevine, not even the seeds or the skins. [Numbers 6:3-4]so when the hour of the crucifixion had come, the vow was still in place and:
they offered him wine to drink, mixed with gall, but when he tasted it, he would not drink it. [Matthew 27:34]However, after the hours of darkness were passed
… Jesus, knowing that all was now finished, said (to fulfill the Scripture), "I thirst." 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. [John 19:28-29]so that anyone who knew that he had taken the vow could see that the time of his separation was ended and the kingdom of God was come.