Jude 1:19

“Those,” he says, “separating” the faithful from the unfaithful, be convicted according to their own unbelief. And again those separating from the flesh. He says, “Animal not having the spirit;” that is, the spirit which is by faith, which supervenes through the practice of righteousness.

And the apostles, who speak of God, in establishing the truth of the advent of the Lord Jesus Christ, have each of them indicated the appearing of these abominable and ruin-working men, and have openly announced their lawless deeds. First of all Peter, the rock of the faith, whom Christ our God called blessed, the teacher of the Church, the first disciple, he who has the keys of the kingdom, has instructed us to this effect: “Know this first, children, that there shall come in the last days scoffers, walking after their own lusts. And there shall be false teachers among you, who privily shall bring in damnable heresies.” After him, John the theologian, and the beloved of Christ, in harmony with him, cries, “The children of the devil are manifest; and even now are there many antichrists; but go not after them. …

50. But those with whom we are arguing, or about whom we are arguing, are not to be despaired of, for they are yet in the body; but they cannot seek the Holy Spirit, except in the body of Christ, of which they possess the outward sign outside the Church, but they do not possess the actual reality itself within the Church of which that is the outward sign, and therefore they eat and drink damnation to themselves. For there is but one bread which is the sacrament of unity, seeing that, as the apostle says, "We, being many, are one bread, and one body." Furthermore, the Catholic Church alone is the body of Christ, of which He is the Head and Saviour of His body. …

30. That they who have separated from the Church have not this Spirit, the Apostle Jude has declared most plainly, saying, “Who separate themselves, natural, having not the Spirit.” Whence the Apostle Paul reproving those even in the Church itself, who by the names of men, though having a place in her unity, were raising a kind of schism, says amongst other things, “But the natural man perceiveth not the things of the Spirit of God, for they are foolishness unto him, neither can he know them, because they are spiritually discerned.” This shows his meaning, “doth not perceive,” that is doth not receive the word of knowledge. These as having a place in the Church, he speaks of as babes, not yet spiritual, but still carnal, and such as are to be fed with milk, not with meat. …

Therefore the philosophers expressly say that ‘nothing comes out of things that are not’ being “sensual” ( Jude 19 ), and trusting nothing to Faith. And yet these same men, when they happen to say anything great and noble, are caught entrusting it to Faith. For instance, that “God is without beginning, and unborn” ; for reason does not suggest this, but the contrary. And consider, I beseech you, their great folly. They say that God is without beginning; and yet this is far more wonderful than the [creation] out of things that are not. For to say, that He is without beginning, that He is unborn, neither begotten by Himself nor by another is more full of difficulties, than to say that God made the things which are, out of things which are not. For here there are many things uncertain: as, that some one made it, that what was made had a beginning, that, in a word, it was made. …