[Paul] censures [the false teachers] ambition; he reproves them for transforming the gospel into human philosophy; he shows that they are destitute of the efficacy of the Spirit, inasmuch as they are taken up with mere ornaments of speech, and seek after a mere dead letter; but not a word is there as to a single false doctrine. Hence I conclude that they were persons who did not openly take away any thing from the substance of the gospel, but, as they burned with a misdirected eagerness for distinction, I am of opinion that, with the view of making themselves admired, they contrived a new method of teaching, at variance with the simplicity of Christ. This must necessarily be the case with all that have not as yet thrown off self, that they may engage unreservedly in the Lord’s work. The first step towards serving Christ is to lose sight of ourselves, and think only of the Lord’s glory and the salvation of men. Farther, no one will ever be qualified for teaching that has not first himself tasted the influence of the gospel, so as to speak not so much with the mouth, as with the dispositions of the heart. Hence, those that are not regenerated by the Spirit of God — not having felt inwardly the influence of the gospel, and know not what is meant when it is said that we must become new creatures, (John 3:7) have a dead preaching, whereas it ought to be lively and efficacious; and, with the view of playing off their part, they disfigure the gospel by painting it over, so as to make it a sort of worldly philosophy.
– Introductory Argument to Commentary on 1st Corinthians