Genesis 21:1 The Lord visited Sarah as he had said, and the Lord did to Sarah as he had promised. And Sarah conceived and bore Abraham a son in his old age at the time of which God had spoken to him. Abraham called the name of his son who was born to him, whom Sarah bore him, Isaac. And Abraham circumcised his son Isaac when he was eight days old, as God had commanded him. Abraham was a hundred years old when his son Isaac was born to him. And Sarah said, “God has made laughter for me; everyone who hears will laugh over me.” And she said, “Who would have said to Abraham that Sarah would nurse children? Yet I have borne him a son in his old age.”
Isaac was a result of a promise from God. This promise was viewed with doubt and seems to be in our nature too. God gives us promises and we doubt Him. Because we doubt either, Him able, or our worthiness, or both, we find ourselves living defeated because we choose doubt, disbelief, and skepticism. We choose to believe the lies of Satan that rather than the truth of God’s steadfast grace, mercy, and love. Do we put time limits on God’s promises? Do we put natural boundaries on the Creator? Do we put human limits on a limitless God?
Matthew Henry has some great thoughts on this.
God’s promised mercies will certainly come at the time which He sets, and that is the best time. When the Sun of comfort is risen upon the soul, it is good to remember how welcome the dawning of the day was. When Sarah received the promise, she laughed with distrust and doubt. When God gives us the mercies we began to despair of, we ought to remember with sorrow and shame our sinful distrust of his power and promise, when we were in pursuit of them. This mercy filled Sarah with joy and wonder. God’s favors to his covenant people are such as surpass their own and others’ thoughts and expectations: who could imagine that he should do so much for those that deserve so little? Who would have said that God should send his Son to die for us, his Spirit to make us holy, his angels to attend us? Who would have said that such great sins should be pardoned, such mean services accepted, and such worthless worms taken into covenant?