He didn't (choose otherwise),
When we're discussing wills, whether someone follows through with their will is largely irrelevant.
but he had the choice. He just did not choose it. He himself freely (although we can debate just how free he was; but that would have more to do with ethics or sin, than with metaphysics or ontology) did not choose otherwise.
Which means that God did not infallibly know the future.
No, that doesn't follow at all. Why could not Jesus see what Peter freely was going to choose to do?
I recommend reading this article on the overall subject. It presents the logical reasoning for why Peter could not have had a choice if Jesus infallibly knew what Peter would do (or, vice versa, why Jesus could not have known infallibly what Peter would do if Peter had/has a will.
I understand where you're coming from I think, so my challenge to you is the timing of choices that we make.
I think it's pretty cut and dried.
For example, if God says "I will without fail do X" (and in scripture, He did that at least a few times), and then later repents (turns away from) of doing that very thing, then there's only two possibilities, as far as I can tell (feel free to present a third):
Either
God never actually intended to do that which He said He did, because He knew that He was never going to do it (the "infallible foreknowledge" bit), which makes Him a liar.
OR
God fully intended to do that which He said He would do, and would have done it, but for the fact that something else is in play, namely, what He says in Jeremiah 18, that if circumstances change, He can no longer do that which He said He would do for whatever the reason may be. This makes God out to be not only just, but also capable, not a liar, but honest and righteous, and more importantly, depending on the situation, merciful and gracious!
And I'm suggesting there's a distinction in time between when we make or determine to make a decision, and when that decision or free choice is materialized in the world.
The ENTIRE BOOK of Jonah speaks to the irrelevance of this distinction.
God said to Nineveh, "In forty days you will be destroyed."
As
@Arthur Brain keeps pointing out with the passage regarding Peter, that is an extremely specific prophecy, with, like with Peter, NO conditions set as to negating what will happen. God fully intended to destroy them.
But guess what happened forty days later.
At the end of the forty days, Jonah went up on a hill to watch them burn, but the fire never fell from heaven, and so He got mad at God for not following through with what He said He would do.
The entire book of Jonah shows that the nation repented, even the king put on sackcloth and sat in ashes! The entire nation repented towards God! Here's the result, as it relates to this topic:
Then God saw their works, that they turned from their evil way;
and God relented from the disaster that He had said He would bring upon them, and He did not do it. - Jonah 3:10
http://www.biblegateway.com/passage/?search=Jonah3:10&version=NKJV
GOD IS MERCIFUL, is He not?
He explains to Jonah:
But the Lord said, “You have had pity on the plant for which you have not labored, nor made it grow, which came up in a night and perished in a night.And should I not pity Nineveh, that great city, in which are more than one hundred and twenty thousand persons who cannot discern between their right hand and their left—and much livestock?” - Jonah 4:10-11
http://www.biblegateway.com/passage/?search=Jonah4:10-11&version=NKJV
God is saying that if circumstances change, then He no longer has to follow through with what He said He would do.
That means God is free!
And if God is free, and we are made in the image of our Creator, then we are also free!
And if we are free, then the future is not set in stone, not all of it, at least.
I choose today to eat chocolate ice cream the very next time that the opportunity to eat chocolate ice cream presents itself to me; but I also choose today to never pursue chocolate ice cream for its own sake. In other words I trust that at some point before I die, chocolate ice cream is going to present itself to me without me having to try, either a birthday party, or a friend suggesting let's go out for ice cream tonight, or a church social----I have faith it's going to happen without any effort on my part. But I determine now, to partake of that chocolate ice cream whenever it does present itself to me.
This is the same sort of reasoning used by those who say "Nineveh wasn't destroyed at the end of Jonah, but it was destroyed later, and so that's what God really meant," ignoring that God intended to destroy Nineveh at the end of the forty days when Jonah preached, not in the future.
If Jesus knows this, then why couldn't He look ahead and see the next time chocolate ice cream heads my way (which is being able to see my future circumstances, not necessarily to see my future choices), and know that I will be eating it then?
Because of this (change out "answering the phone" with "eating ice cream"):
I again demonstrated that this is untrue. Unless you're willing to admit that I myself in determining now, to eat chocolate ice cream in the future, whenever it presents itself to me in the future, if I am physically capable of eating it then: that I have simultaneously rendered my future choice capable of foreknowledge, and nullified my will.
This is why Open Theists refocus the argument on whether God is free, because it makes it a lot easier to answer question like this, hence my post earlier about God being the one to eat the ice cream.
If you can't agree to this, then I don't think you quite understand the meaning of the terms you're using. If I have chosen to eat ice cream, then am I no longer free anymore, because I have actually made a choice? That makes zero sense.
Rather, you are free up until you eat the ice cream to choose not to eat it. Heck, you can even spit the ice cream out before you swallow it. That's how free you are.
That necessitates that freedom is just a constant state of indecision, and that once you make a choice, you are no longer free.
Only when that choice is turned into action. We're talking about just having the choice, however. The "action on that choice" comes later.
This is the opposite of what Jesus said about knowing the truth. We're going to be set free. So making a choice cannot equal losing our freedom; we will gain our freedom when we make the right choice.
It doesn't equal losing our freedom. It equals exercising our freedom.
