12 How great a boon of God this is, and how great a blessing of matrimony is clear from a consideration of man's dignity and of his sublime end. For man surpasses all other visible creatures by the superiority of his rational nature alone. Besides, God wishes men to be born not only that they should live and fill the earth, but much more that they may be worshippers of God, that they may know Him and love Him and finally enjoy Him for ever in heaven; and this end, since man is raised by God in a marvelous way to the supernatural order, surpasses all that eye hath seen, and ear heard, and all that hath entered into the heart of man. From which it is easily seen how great a gift of divine goodness and how remarkable a fruit of marriage are children born by the omnipotent power of God through the cooperation of those bound in wedlock.
Source: Casti Connubii (Vatican.va)