From The Orthodox Open Theist:
As Open Theists we see God has having free will and freely creating morally capable beings with free will, so that we might engage in a free and loving relationship with God. That means letting go of the idea that God is always defined by attributes.
So, what’s the alternative? Free will, of course. You see, God loves, not because it is His nature to love, but rather because love is the means by which God chose to enter into relationship with us. In the same way, God is just in that God chooses to be sovereign over creation, not because it is an attribute of God. God is freely just in the same way that he freely loves.
Ultimately, this is the only way that God is completely God. If God’s attributes determine God’s behavior, then He is not omnipotent, as He cannot violate what His attributes force Him to do. That’s the complete God Open Theism needs.