5 But wherefore does he call it a “book of the generation of Jesus Christ,” while yet this book has not the birth only, but the whole dispensation? Because this is the sum of the whole dispensation, and is made an origin and root of all our blessings. As then Moses calls it the book of heaven and earth, although he has not discoursed of heaven and earth only, but also of all things that are in the midst thereof; so also this man has named his book from that which is the sum of all the great things done. For that which teems with astonishment, and is beyond hope and all expectation, is that God should become man. But this having come to pass, all afterwards follows in reasonable consequence.
Source: Homilies on the Gospel of St. Matthew (New Advent)