John Wesley on Genesis 22:12

Lay not thine hand upon the lad - God's time to help his people is, when they are brought to the greatest extremity: the more eminent the danger is, and the nearer to be put in execution, the more wonderful and the more welcome is the deliverance. Now know I that thou fearest God - God knew it before, but now Abraham had given a memorable evidence of it. He need do no more, what he had done was sufficient to prove the religious regard he had to God and his authority. The best evidence of our fearing God is our being willing to honour him with that which is dearest to us, and to part with all to him, or for him.