The conclusion of Pope Pius XI’s encyclical Quas Primas (1925):
The faithful, moreover, by meditating upon these truths, will gain much strength and courage, enabling them to form their lives after the true Christian ideal. If to Christ our Lord is given all power in heaven and on earth; if all men, purchased by his precious blood, are by a new right subjected to his dominion; if this power embraces all men, it must be clear that not one of our faculties is exempt from his empire. He must reign in our minds, which should assent with perfect submission and firm belief to revealed truths and to the doctrines of Christ. He must reign in our wills, which should obey the laws and precepts of God. He must reign in our hearts, which should spurn natural desires and love God above all things, and cleave to him alone. He must reign in our bodies and in our members, which should serve as instruments for the interior sanctification of our souls, or to use the words of the Apostle Paul, as instruments of justice unto God.35 If all these truths are presented to the faithful for their consideration, they will prove a powerful incentive to perfection. It is Our fervent desire, Venerable Brethren, that those who are without the fold may seek after and accept the sweet yoke of Christ, and that we, who by the mercy of God are of the household of the faith, may bear that yoke, not as a burden but with joy, with love, with devotion; that having lived our lives in accordance with the laws of God’s kingdom, we may receive full measure of good fruit, and counted by Christ good and faithful servants, we may be rendered partakers of eternal bliss and glory with him in his heavenly kingdom.
Let this letter, Venerable Brethren, be a token to you of Our fatherly love as the Feast of the Nativity of Our Lord Jesus Christ draws near; and receive the Apostolic Benediction as a pledge of divine blessings, which with loving heart, We impart to you, Venerable Brethren, to your clergy, and to your people.
Given at St. Peter’s Rome, on the eleventh day of the month of December, in the Holy Year 1925, the fourth of Our Pontificate.
35 Rom. vi, 13.
— Quas Primas 33-34