Passover, the Last Supper and the Four Cups

This is a little bit of thinking while I write prompted by my revision for my Moore College New Testament 1 exam. Apparently, during the celebration of Passover, every person would be expected to drink four cups of wine. This represents the four "I will" statements that can be found in Exodus 6:6-7.

"Say therefore to the people of Israel, 'I am the LORD, and I will bring you out from under the burdens of the Egyptians, and I will deliver you from slavery to them, and I will redeem you with an outstretched arm and with great acts of judgment. I will take you to be my people, and I will be your God, and you shall know that I am the LORD your God, who has brought you out from under the burdens of the Egyptians."

Exodus 6:6-7

So a cup of wine would have been drunk to remember each of God's promises in these verses - he will bring them out from under their burden, he will deliver them from slavery, he will redeem them and finally he will take them to be his people. These cups would have been drunk at various points during the Passover meal - the first before the Grace before the meal, the second during the meal over which the story of the passover would be told, the third during the Grace after the meal and the last was drunk before the singing of a final hymn at the end of the meal.

A few of the commentaries I've been looking at comment that at the Last Supper, which of course was a Passover meal, Jesus did not drink the last cup, a cup that was sometimes referred to as the "Cup of Consummation". If we were to look at the account of the Last Supper from Mark chapter 14, Jesus says after the distribution of bread and wine:

"Truly, I say to you, I will not drink again of the fruit of the vine until that day when I drink it new in the kingdom of God.""

The next thing that happens in v. 26 is they sign a hymn and then go to the Garden of Gethsemane. The commentators argue that Jesus' specific mentioning of not drinking wine again is of cultural significance, saying that the disciples would have realised that he was referring to fulfilling what the final cup was pointing to - God's taking of his people.

I'm not sure I'm convinced, but that's a summary of what little I've looked at. It's certainly an interesting point if it could be shown a little more clearly, and another slight problem is that today, there are actually five cups, not four. The fifth is kept for Elijah, in anticipation of the Messianic age, and isn't drunk, but I'm reckoning that might be a more recent addition...