Christ is truly our Redeemer

You were redeemed with the precious blood of Christ, as of a lamb unspotted and undefiled.
1Pe. 1, 19

By the sin of our first parents, the whole human race was alienated from God, as is taught in the second chapter of the epistle to the Ephesians. It was not from God's power that we were thereby cut off, but from that sight of God's face to which His children and His servants are admitted.

Then again we descended beneath the usurped power of the devil. Man had consented to the devil's will and, thereby, had made himself subject to the devil; subject, that is to say, as far as lay in man's power, for since he was not his own property, but the property of another, he could not really give himself away to the devil.

By His Passion, then, Christ did two things. He freed us from the power of the enemy, conquering him by virtues which were the very contraries to the vices by which he had conquered man — by humility, namely, by obedience and by an austerity of suffering that was in direct opposition to the enjoyment of forbidden food.

Furthermore, by making satisfaction for the sin committed, Christ joined man with God and made him the child and servant of God.

This emancipation had about it two things that make it a kind of buying. Christ is said to have bought us back or to have redeemed us inasmuch as he snatched us from the power of the devil, as a king is said, by hard-fought battles, to re deem his kingdom that the enemy has occupied. Christ is again said to have redeemed us inasmuch as He placated God for us, paying as it were the price of His satisfaction on our behalf, that we might be freed both from the penalty and from the sin.

This price, His precious blood, he paid — that he might make satisfaction for us — not to the devil but to God. Again, by the victory that His Passion was, he took us away from the devil.

The devil had indeed had dominion over us, but unjustly, since what power he had was usurped. Nevertheless, it was but just that we should fall under his yoke, seeing that it was by him we were overcome. This is why it was necessary that the devil should be overcome by the very contrary of the forces by which he had himself overcome. For he had not overcome by violence, but by a lying persuasion to sin.

(3 Dist. 19 91, a 4.)