God is free to act according to His nature, as are humans. He is not free to do evil because that is contrary to His nature. He is not free to make a squared circle or a rock that is too heavy for Him to move. The point of the verse is that God will accomplish His will in every situation, no matter what man does. God is free to do what He pleases because it is heaven that rules, not man. He saves whom He wills and leaves the rest to perish in their sins.
Discussion
I agree with all of that as you presented it.
God can do something new. Right?
He can create a new butterfly or write a new song. None of that would violate his nature.
Numbers 16:30-31 But if the LORD creates something new, and the ground opens its mouth and swallows them up with all that belongs to them, and they go down alive into Sheol, then you shall know that these men have despised the LORD.”
And as soon as he had finished speaking all these words, the ground under them split apart.
God can do something new. Don't you think?
#opentheism