6 The Lord warns us in His Gospel, saying, “You reject the commandment of God, that you may establish your own tradition.” Let them who reject the commandment of God and endeavour to keep their own tradition be bravely and firmly rejected by you; let one downfall be sufficient for the lapsed; let no one by his fraud hurl down those who wish to rise; let no one cast down more deeply and depress those who are down, on whose behalf we pray that they may be raised up by God's hand and arm; let no one turn away from all hope of safety those who are half alive and entreating that they may receive their former health; let no one extinguish every light of the way of salvation to those that are wavering in the darkness of their lapse.
The apostle instructs us, saying, “If any man teach otherwise, and consent not to the wholesome words of our Lord Jesus Christ and His doctrine, he is lifted up with foolishness: from such withdraw yourself.” And again he says, “Let no man deceive you with vain words; for because of these things comes the wrath of God upon the children of disobedience. Be not therefore partakers with them.” There is no reason that you should be deceived with vain words, and begin to be partakers of their depravity.
Depart from such, I entreat you, and acquiesce in our counsels, who daily pour out for you continual prayers to the Lord, who desire that you should be recalled to the Church by the clemency of the Lord, who pray for the fullest peace from God, first for the mother, and then for her children. Join also your petitions and prayers with our prayers and petitions; mingle your tears with our wailings. Avoid the wolves who separate the sheep from the shepherd; avoid the envenomed tongue of the devil, who from the beginning of the world, always deceitful and lying, lies that he may deceive, cajoles that he may injure, promises good that he may give evil, promises life that he may put to death.
Now also his words are evident, and his poisons are plain. He promises peace, in order that peace may not possibly be attained; he promises salvation, that he who has sinned may not come to salvation; he promises a Church, when he so contrives that he who believes him may utterly perish apart from the Church.
Source: The Epistles of Cyprian (New Advent)