St. John Chrysostom: The Duty of Fraternal Correction

Consider to what a dignity he exalts himself who esteems his brother's salvation as of great importance. Such a man is imitating God as far as lies with the power of man. Hear what God says speaking through His prophet: "He who separates the worthy from the vile shall be as My mouth." (Jer 15:19)  What He says is that he who is eager to save a brother who has fallen into careless ways, he who hastens to snatch his brother from the jaws of the devil, that man imitates me as far as lies in human power. What could equal that? This is greater than all good deeds. This is the peach of all virtue.
+St. John Chrysostom, from Baptismal Instructions, The Sixth Instruction, The Gravity of Scandal and the Duty of Fraternal Correction #19.