Thy kingdom come, thy will be done
… It has long been a common custom to give Christ the metaphorical title of King, because of the right degree of perfection whereby he excels and surpasses all created beings. For as it is the case, that he is said to reign in the souls of men, not so much by reason of the keenness of his intellect and the extent of his knowledge, as that he himself is the Truth; so it is from him that truth must be drawn, and obediently received by all mankind. He reigns, likewise, in the wills of men, since not only does the integrity and the obedience of the human will accord exactly and precisely with the holiness of the divine will in him, but also by his grace and inspiration, he substitutes this for our free will, whereby we may be enkindled to every noblest deed. In a word, Christ is acknowledged as the King of hearts, on account of his charity which surpasses understanding, and of his mercy and kindness, which draw to him the souls of men. Never has it happened that anyone has been loved as much at any time as Christ Jesus is loved by so many different races, never will it happen in time to come that anyone shall be so loved. But, if we ponder this matter more deeply, we cannot but see, that the title and the power of a King is rightly claimed for Christ as a man, in the strict and proper sense of the word. For, only so far as he is man, can he be said to have received the power and the glory and the kingdom from the Father, seeing that the Word of God, which is of the same substance as the Father, cannot fail to have all things in common with the Father, and therefore has in itself the highest and most absolute dominion over all things created.
– From the Encyclical Letter of Pope Pius XI, Quas Primas, December 11, 1925, from: An Approved Translation of the Breviarium Romanum, Burns & Oates, London, 1964