By faith, barren Sarah was able to become pregnant, old woman as she was at the time, because she believed the One who made a promise would do what he said.
Hebrews 11:11 (MSG)
We are often called to leave worldly connexions, interests, and comforts. If heirs of Abraham’s faith, we shall obey and go forth, though not knowing what may befall us; and we shall be found in the way of duty, looking for the performance of God’s promises. The trial of Abraham’s faith was, that he simply and fully obeyed the call of God. Sarah received the promise as the promise of God; being convinced of that, she truly judged that he both could and would perform it. Many, who have a part in the promises, do not soon receive the things promised. Faith can lay hold of blessings at a great distance; can make them present; can love them and rejoice in them, though strangers; as saints, whose home is heaven; as pilgrims, travelling toward their home. By faith, they overcome the terrors of death, and bid a cheerful farewell to this world, and to all the comforts and crosses of it. And those once truly and savingly called out of a sinful state, have no mind to return into it. All true believers desire the heavenly inheritance; and the stronger faith is, the more fervent those desires will be. Notwithstanding their meanness by nature, their vileness by sin, and the poverty of their outward condition, God is not ashamed to be called the God of all true believers; such is his mercy, such is his love to them. Let them never be ashamed of being called his people, nor of any of those who are truly so, how much soever despised in the world. Above all, let them take care that they are not a shame and reproach to their God. The greatest trial and act of faith upon record is, Abraham’s offering up Isaac, Ge 22:2. There, every word shows a trial. It is our duty to reason down our doubts and fears, by looking, as Abraham did, to the Almighty power of God. The best way to enjoy our comforts is, to give them up to God; he will then again give them as shall be the best for us. Let us look how far our faith has caused the like obedience, when we have been called to lesser acts of self-denial, or to make smaller sacrifices to our duty. Have we given up what was called for, fully believing that the Lord would make up all our losses, and even bless us by the most afflicting dispensations? Matthew Henry