Now the LORD was gracious to Sarah as he had said, and the LORD did for Sarah what he had promised. Sarah became pregnant and bore a son to Abraham in his old age, at the very time God had promised him. Abraham gave the name Isaac to the son Sarah bore him. Genesis 21:1-3
God is in the impossible business. As a Christian, whatever you face, no matter how impossible it may seem, God will walk with you through the situation. He may resolve it, restore it, remove it, but at a minimum, He will always be there with you, somehow causing all things to work together for good. It may not be the good you want, but in retrospect it will always be the good you need.
For Sarah it was giving birth to an heir for Abraham, even though she was well past child bearing age. Hebrews 11:11 tells us by faith Sarah was enabled to bear children because she considered God faithful who made the promise (of making a great nation out of Abraham’s descendants), though he had no descendants before this time. Thousands of years later, a young Hebrew woman will give birth to a son, a spiritual heir to Abraham, though she is still a virgin. With God nothing is impossible.