What is the significance of 2 Kings 20:1–7?

The Lord tells Hezekiah “[Y]ou shall die: you shall not recover” (vs. 1). Hezekiah pleads with God and God says, “I will add fifteen years to your life” (vs. 6).

If everything about the future was exhaustively settled and known by God as such, his prophecy to Hezekiah that he was going to die would have been manipulative and his declaration that he was now adding years to his life inaccurate. The prophecy is straightforward only if it expresses God’s true intention at the time he gave it. And for this to be possible it could not have been an eternally foregone conclusion that he was going to spare Hezekiah’s life.