And Sarah saw the son of Hagar the Egyptian, which she had born unto Abraham, mocking. Wherefore she said unto Abraham, Cast out this bondwoman and her son: for the son of this bondwoman shall not be heir with my son, even with Isaac.
The spiritual meaning of this never could have been known, had not the Holy Ghost graciously condescended to have taught the Church, by his servant the apostle. See Galatians 4:2-31.