II. Christ's victory has won back many to the Faith.
Exult therefore, beloved brother, yes, exult triumphantly in the only-begotten Son of God. Through us He has conquered for Himself the reality of Whose flesh was denied. Through us and for us He has conquered, in whose cause we have conquered. This happy day ranks next to the Lord's Advent for the world. The robber is laid low, and there is restored to our age the mystery of the Divine Incarnation which the enemy of mankind was obscuring with his chicaneries, because the facts would not let him actually destroy it.
Nay, the immortal mystery had perished from the hearts of unbelievers, because so great salvation is of no avail to unbelievers, as the Very Truth said to His disciples: “he that believes and is baptized shall be saved; but he that believes not shall be condemned.” The rays of the Sun of Righteousness which were obscured throughout the East by the clouds of Nestorius and Eutyches, have shone out brightly from the West, where it has reached its zenith in the Apostles and teachers of the Church.
And yet not even in the East is it to be believed that it was ever eclipsed where noble confessors have been found among your ranks: so that, when the old enemy was trying afresh, through the impenitent heart of a modern Pharaoh, to blot out the seed of faithful Abraham and the sons of promise, he grew weary, through God's mercy, and could harm no one save himself. And in regard to him the Almighty has worked this wonder also, in that He has not overwhelmed with the founder of the tyranny those who were associated with him in the slaughter of the people of Israel, but has gathered them into His own people; and as the Source of all mercy knew to be worthy of Himself and possible for Himself alone, He has made them conquerors with us who were conquered by us.
For while the spirit of falsehood is the only true enemy of the human race, it is undoubted that all whom the Truth has won over to His side share in His triumph over that enemy. Assuredly it now is clear how divinely authorized are these words of our Redeemer, which are so applicable to the enemies of the Faith that one may not doubt they were said of them: “You,” He says, “are of your father the devil, and the lusts of your father it is your will to fulfil. He was a murderer from the beginning and stood not in the truth, because the truth is not in him. When he speaks a lie, he speaks of his own: for he is a liar and the father thereof.”
Source: Letters (New Advent)