S – The Lord came to Sarah as he had said, and the Lord did for Sarah what he had promised. ² Sarah became pregnant and bore a son to Abraham in his old age, at the appointed time God had told him

Genesis 21:1–2 CSB

O – Commentary:

The name Isaac (Hebrew yitskhaq) means “he laughs.” Sarah’s wordplay shows that the laughter of unbelief when the promise was given (18:12) had changed to the laughter of joy at its fulfillment. Isaac’s name could refer to the pleasure of God and of his parents at his birth. Sarah knew that everyone who heard about this would laugh with her and rejoice at the news.

 New Living Translation Study Bible 

A – God has plans and a purpose for each of us.  He will do what he has promised.  Sarah’s laughter of disbelief is “How can do this?” changes to honor, gratitude and reverence to God asking “How can God do this?”  We will experience similar emotions as we walk with God as we remain faithful.

R – Heavenly Father, you are all powerful and all knowing.  Empower our faith today.  Give us the ability to believe even when it seems impossible.  There are no limits on what you can do – don’t let us put them on you with our disbelief.