In the name of the Father and of the +Son and of the Holy Spirit, Amen.
Isaac was a man of God. Literally. He existed because of God’s miraculous action. His father, Abraham, was 100 years old (Gen. 21:5) and his mother 90 (Gen. 17:17) when he was born. This was long before in vitro fertilization or fertility drugs. There was no scientific intervention. It was pure miracle. The Lord’s promise fulfilled by the Lord’s gracious intervening in the lives of us mere mortals. Now Isaac, the inheritor of God’s promise (Gen. 17:19), to make Abraham a great nation and bless all the families of the earth through Abraham's offspring (Gen. 12:2-3), gets married at 40. (Gen. 25:20) They had a habit of putting things off in this family. But The Lord had promised. So biological clocks don’t matter when the Lord promises you’ll have kids. Except when you run up against cold, hard reality: Rebekah was barren. Infertile. Try though they might, they couldn’t conceive. So Isaac cries out to the Lord. He reminds Him of His promises. He stands in faith on what God Himself had said to him. The Lord is true to His word. She who was barren conceives. (Gen. 25:21)