Sarah’s elevation above Abraham in the things of the kingdom of God is now to appear in illustration of all this. In obedience to the command, Abraham calls the child that was born, Isaac. But Sarah _interprets_ that name: and this is a finer exercise of soul over the gift of God. To obey a word is good; but to obey it in the joy of an exercised heart, and in the light and intelligence of a mind that has entered into the divine sense of that word, is better. Abraham called the child that was born to him, Isaac: but Sarah said "God has made me to laugh; and all they that hear it will laugh with me." The oracle of chapter xvii. 19 was made more to her than a command to be observed. It had springs of refreshing in it, and kindlings of soul. It was full of light and meaning to the opened understanding of Sarah. And this leads to strength and decision. This Deborah of earlier days will brace the loins of Barak. "Cast out this bondwoman and her son," says Sarah to Abraham; for she was happy in the liberty of grace and promise, while he was still lingering amid the claims of nature, and the desires which his own loins had gendered. "Cast out this bondwoman and her son; for the son of this bondwoman shall not be heir with my son, even with Isaac." And this was _Scripture_, as we read in Gal. iv.; this was the voice of God. This decision of faith, in the liberty of grace, gets its sealing at once under God’s own hand. "Stand fast in the liberty wherewith Christ hath made you free," says the Spirit. And what met the mind of the Lord, in the days of His flesh, like the faith which was bold and free, after this manner? the faith which would use Him without ceremony, which reached Him through a crowd, which pressed in through the silent reproaches of a misjudging Pharisee, or through the injurious whispers of a self-righteous multitude! And how much of the energy of the Spirit in St. Paul is engaged in giving the sinner this precious boldness, this immediate assurance of heart in Christ, in spite of law, conscience, earth, and hell!
This boldness of faith in Sarah, this challenge of the bondwoman, this demand (in her own behalf too) that she might enjoy her Isaac all alone, is _Scripture_. Gal. iv. 30. She spake as "the oracles of God." But in Abraham nature now acts. He would fain retain Ishmael. This is no strange thing. Nature now acts in Abraham, and faith in Sarah; as, on an earlier occasion, which we noticed, nature had acted in Sarah and faith in Abraham. But nature in Abraham must submit. He must not let Sarah be entangled any longer as with this yoke of bondage. The house must be freed of Ishmael, for it is to be built only in Isaac. "The son of the bondwoman shall not be heir with the son of the freewoman."