Matthew Poole and continuators on Galatians 6:3

3 For if a man think himself to be some thing when he is nothing, he deceiveth himself .

It is a general maxime, and the truth of it is obvious to every one that readeth it, for supposing a man to be nothing of what he thinks himself to be, he must needs deceive himself in nourishing and entertaining such an Opinion of himself. For the dependance of it upon what the Apostle had said before, it is obvious. Pride and mens high opinions of themselves above what they ought, are the cause of their censoriousness, and morosity in dealing with other offenders; which modesty would not suffer in them, if they apprehended themselves to be as weak, and as much exposed to Temptations as others are. It is Pride and overweening opinions of our selves, that make us despise or neglect to others, under their burdens, and so forget the Law of Christ; the Apostle therefore properly addeth this precept for humility, and modesty to these former precepts.

Marginal references: 1 Cor. 8.2.