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 among other things, “But the natural man perceives 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, “does not perceive,” that is does 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. “Even,” he says, “as unto babes in Christ, have I given you milk and not meat; for hitherto you were not able to bear it, neither yet now are you able.” When we say, “not yet,” we must not despair, if that which is “not yet” tends to be. For he says, “you are yet carnal.” And showing how it is that they are carnal, he says, “For whereas there is among you envying, and strife, and divisions, are you not carnal, and walk as men?”
And again more plainly, “For while one says, I am of Paul, and another, I of Apollos, are you not carnal? Who then is Paul, and who is Apollos, but ministers by whom you believed?” These then, that is, Paul and Apollos, agreed together in the unity of the Spirit and the bond of peace; and yet because the Corinthians began to divide them among themselves, and “to be puffed up for one against another,” they are said to be men— carnal and natural men, not able to receive the things of the Spirit of God; and yet because they are not separated from the Church, they are called “babes in Christ;” for indeed he desired that they should be either Angels, or even Gods, whom he reproved because they were men, that is, in those contentions, “They savoured not the things which be of God, but the things which be of men.” But of those who are separated from the Church it is not merely said, “perceiving not the things of the Spirit of God,” lest it should be referred to the perception of knowledge; but it is said, “Having not the Spirit.”
For it does not follow, that he who has it, should also by knowledge perceive what he has.
Source: Sermons on Selected Lessons of the New Testament (New Advent)