Sarah followed Abraham and together they obeyed God not knowing where they were going. Abram took his wife Sarai and his nephew Lot with him, along with all the possessions and people they had gotten in Haran, and set out for the land of Canaan and arrived safe and sound. (Abraham was 75 years old, so that would make Sarah about 65, if you consider she was 90 and he was 100 when their promised son was born.)
It might be compared in some ways to a farmer these days, packing up the house, the barn, the animals and all he and his family possess and moving to another farm in another state—but they didn’t know where they were going. They just stepped out trusting in God to deliver all He promised.
Throughout Sarah’s story, there are many challenges. She and her husband were ordinary people trusting God for something greater than they could ask or think. They were far from perfect—just like us. They had their moments of doubt and unbelief along the way.
Sarah struggled to believe God’s promises included her. The natural circumstances crowded into her thinking as month after month, year after year she remained childless. It was a common practice in their time and culture to give a maidservant as a substitute wife to the husband, but remember, God had called them out from their people. He set them apart to follow Him and live according to His ways. He desired for their lives to look differently from the rest of the world.
God had a plan, but Sarah decided to help God out. Sarah encouraged her husband to follow the culture of her day and to sleep with her maidservant, Hagar. Sarah probably thought she could raise the child as her own. Abraham agreed and acted on Sarah’s plan. Once Hagar became pregnant, Sarah and Hagar’s relationship quickly changed. Hagar detested Sarah, and Sarah resented the woman who was able to give her husband the one thing she didn’t think she could give him.
The Lord appeared to Abraham when he was 98 years old and told him this time next year, I will return to you and Sarah will have a son. Sarah overhead the conversation and laughed at His words. The Lord confronted her asking why she laughed, and she fearfully lied that she didn’t laugh. The Lord again said, “Yes, You did laugh.”
When we hatch our own plan to help God deliver on His promise, or hurry things along outside of His plan, those consequences can have lasting effects. Problems continued between Sarah and Hagar even after Sarah gave birth to the child God promised. (Even today the descendants of Ismael and Isaac continue to war against one another.)
Yet Hebrews 11:11 says, By faith Sarah herself received power to conceive, even when she was past the age, since she considered him faithful who had promised. God is telling Sarah’s story from “the end.” It doesn’t matter to God how many times she stumbled, how many times she failed. It doesn’t matter to him that she laughed in doubt or tried to take matters into her own hands. In the end, she saw God’s promises for her life delivered. She became what He created her to be all along—a mother of a great nation. She believed God and walked with Him by faith.
If you’ve ever waited on a promise, you probably found it very challenging. Even if you’re a very patient person, it’s difficult to cope with a long wait. I know I spend a lot of time thinking about the thing God promised and wondering just how God will pull it all together.
 Genesis 12:5 MSG
 Genesis 18:10-15 NIV