Abraham knew without a doubt that Isaac was from God -- that God had given Isaac to him (Genesis 17). Yet then God said, sacrifice him. Give him up. Let him go. He was the promise child, the answer to their prayers, the gift of God. And God said, let go of him. Abraham's response was obedience. It was "God knows what He's doing," and trust in Him. Abraham was committed to obey the Lord.
The result... it was a test of Abraham's faith, loyalty, and obedience. It strengthened his faith! It demonstrated his commitment. And Isaac remained, because God stepped in. "Now I know that you fear God, since you have not withheld your son." (Genesis 22:12)
"Until God had Isaac, He did not have all of Abraham there was to have." --sermon notes
Sometimes God finds it necessary to loosen our grip on certain things, things we may be holding too tightly. He might, in His sovereignty, take it away completely...or He might, in His lovingkindess, let it remain. But we have a tendency to keep too tight a grip on the things we care about -- a job, a relationship, security, money, our plans, etc. We want to hang on, because we're scared if we let go, God will take it away.
But clinging isn't pretty. Neither is God having to literally pry it out of our white-knuckled hands. Surrender is hard, but beautiful. The story will be much better if we loosen our fists and let God do His thing in His time, and trust that the results will be His good and perfect will. "Hold all things loosely."