Roman Catechism 4.26

Chapter 4 — Part I: The Creed — Article II: And in Jesus Christ, His Only Son, Our Lord

Section 26. He is also called Lord because in one Person both natures, the human and the divine, are united; and even though He had not died for us, He would have yet deserved, by this admirable union, to be constituted common Lord of all created things, particularly of the faithful who obey and serve Him with all the fervour of their souls.