'...couples who cannot conceive because of infertility can still aim to make children followers of Jesus. God's purpose in making marriage the place to have children was never merely to fill the earth with people, but to fill the earth with worshippers of the true God. One way for a marriage to fill the earth with worshippers of the true God is to procreate and bring the children up in the Lord. But that's not the only way. When the focus of marriage becomes "Make disciples of Jesus," the meaning of marriage in relation to children is not mainly "Make them," but "Make them disciples." And the latter can happen even when the former doesn't.'
John Piper, This Momentary Marriage, p.138.