You all convinced me, I'm now an Atheist!!!

[Esquilax]

It means:
to fulfil, i.e. to cause God's will (as made known in the law) to be obeyed as it should be, and God's promises (given through the prophets) to receive fulfilment

What where those promises?
Prophesy concerning atonement. If you like I have a few sites that can step you through all of these prophesies.

"To cause god's will to be obeyed as it should be"? You mean, the god's will that was laid down in the old testament, for whom the only previous expressions of will that Jesus could be referring to would be in the old testament?

Again, the issue isn't the words, so much as your interpretation of them; your assertion that causing god's will to be obeyed means discarding the previous record of that will is bizarre, and not supported even in the translation you've given here.