The apostle denies that any have rightly learned Christ, who have not been taught that they must put off the old man, which is corrupt according to the deceitful lusts, and put on Christ (Eph 4:20ff).

Their knowledge of Christ, then, is proved to be a false and injurious pretense, with whatever eloquence and volubility they may talk concerning the Gospel.

For it is a doctrine not of the tongue, but of the life.

It is not apprehended merely with the understanding and memory like other sciences, but is then only received, when it possesses the whole soul, and finds a seat and residence in the inmost affection of the heart.

Let them, therefore, either cease to insult God by boasting themselves to be what they are not, or shew themselves disciples not unworthy of Christ their master.

—John Calvin
Institutes of the Christian Religion, III, vi, 4.