9 Whoever compare the pagan and the Christian attitude toward slavery will easily come to the conclusion that the one was marked by great cruelty and wickedness, and the other by great gentleness and humanity, nor will it be possible to deprive the Church of the credit due to her as the instrument of this happy change. And this becomes still more apparent when we consider carefully how tenderly and with what prudence the Church has cut out and destroyed this dreadful curse of slavery. She has deprecated any precipitate action in securing the manumission and liberation of the slaves, because that would have entailed tumults and wrought injury, as well to the slaves themselves as to the commonwealth, but with singular wisdom she has seen that the minds of the slaves should be instructed through her discipline in the Christian faith, and with baptism should acquire habits suitable to the Christian life. Therefore, when, amid the slave multitude whom she has numbered among her children, some, led astray by some hope of liberty, have had recourse to violence and sedition, the Church has always condemned these unlawful efforts and opposed them, and through her ministers has applied the remedy of patience. She taught the slaves to feel that, by virtue of the light of holy faith, and the character they received from Christ, they enjoyed a dignity which placed them above their heathen lords, but that they were bound the more strictly by the Author and Founder of their faith Himself never to set themselves against these, or even to be wanting in the reverence and obedience due to them. Knowing themselves as the chosen ones of the Kingdom of God, and endowed with the freedom of His children, and called to the good things that are not of this life, they were able to work on without being cast down by the sorrows and troubles of this passing world, but with eyes and hearts turned to heaven were consoled and strengthened in their holy resolutions. St. Peter was addressing himself specially to slaves when he wrote: "For this is thanksworthy, if for conscience towards God a man endure sorrows, suffering wrongfully. For unto this you are called; because Christ also suffered for us, leaving you an example that you should follow his steps."(17)
Source: In Plurimis (Vatican.va)