Genesis 21:1 is a remarkable verse of Scripture. Two statements immediately jump out of the text:
“And the LORD visited Sarah as he had said, and the LORD did unto Sarah as he had spoken.” (emphasis added)
What a profound lesson in God’s reliability! God did exactly what He said He would do. Not only that, He did it at the precise time that He had set (v.2). All the way back in Genesis 13:16 God first made the promise that Abraham would have descendants as numerous as the dust of the Earth. Abraham did not have even one single child at the time, but God made this promise to him as if it was already a done deal (Romans 4:17). Despite Abraham and Sarah’s deception with Pharaoh and Abimilech in which Sarah’s purity could have been compromised (Gen. 12:13, 20:2), despite their scheme to bring about the child of promise from the womb of another (Gen. 16), despite Sarah’s laughter at the very notion that she could bring forth a child in her old age (18:12), God visited Sarah as He had said, and did unto her as He had spoken.
Regardless of how things may look to us, God will make good on every promise that He has ever made. He will do what He has said He will do. No one is able to frustrate the plans of God, nor can anyone prevent His promises from coming to pass. God is reliable.