Why was God's promise of a son to Abraham still valid despite his and Sarah's old age?
The promise remained valid because God Himself guaranteed it; what God promises He will not let fail. Although Abraham was nearing 100 and Sarah nearing 90, God declared He would give them a son, Isaac, at the set time, making him a son of promise and of God's miracle-working power.
Les explains that God’s promise could not fail because it rested on God’s own word: what God promises, He is not going to let fail. Even though Abraham was nearing 100 and Sarah nearing 90, the promise remained valid because God said He would do it. God specifically promised a son named Isaac, and He said the covenant would be established with Isaac, whom Sarah would bear at the set time in the next year. Les notes that Isaac was therefore a son of promise and also a son of the miracle-working power of God, since both parents were way beyond normal childbearing.
More Questions
Why was God's promise to Abraham still valid even though he and Sarah were too old to have children?
Even though Abraham was nearing 100 and Sarah nearing 90, God's promise to them remained valid simply because God said He would do it.