John Calvin on Jacob’s wrestling with the Angel of the Lord:
It was God himself [who tested Jacob]. This teaches us that our faith is tried by God, and whenever we are tested, he descends into the arena to try our strength.
At least it is God who tests our faith. At least it is God who tries the strength of our character. If we are to struggle, at least we struggle in the hands of a gracious and kind God because in His hands, there is mercy when we fail and sustaining power when we falter.
A practicing swordsman is better off training with his master than be cast off into the hands of a ruthless enemy in a real combat. In his master’s hands he can learn the art of fighting. In enemy’s hands, he can be destroyed.
The best thing about Jacob’s wrestling with God is that it was God who tried him, not Satan. God means to strengthen us while Satan seeks to destroy us.