But let every man prove his own work
Not concern himself about the actions and works of others; let him review his own heart and actions; let him examine, try, and prove his whole conduct in life by the rule of God's word, when he will find enough at home, without bearing hard upon, and censuring others:
and then shall he have rejoicing in himself
and not in another; which is either ironically said, he will then see what reason he has to rejoice and glory in his own works, and vaunt over others, and to boast of his performances, and despise others; so far from it, that he will have reason to be ashamed of himself, and to own and acknowledge his unworthiness and unprofitableness: or if, upon such a review, examination, and probation of his works, it shall appear that he has had his conversation in the world, by the grace of God, in simplicity and godly sincerity, this testimony of his conscience will be his rejoicing; see ( 2 Corinthians 1:12 ) . He may rejoice "in himself", in his own works, as the fruits of grace, but not as the effects of his own power and strength; and may glory and boast of them before men, in vindication of his cause and character, and as evidences of the truth of grace, but not before God, as if they were the matter of his justification and acceptance:
and not in another;
that is fallen into sin; making use of his sins and faults to set off himself, and to increase his own praise and condemnation; rejoicing in this, that he is better than others, and is not, as the Pharisee said, as other men are, as wicked as they, or has not fallen into such sins as others have done. He will have occasion to take such a method as this, if his conversation will bear the test; he will have rejoicing in the testimony of his own conscience, and will have no need to compare himself with others; his glorying will be on account of his own actions, and not through a comparison of other men's. This no ways contradicts a man's glorying in God, and rejoicing in Christ Jesus alone, in the business of salvation. It only regards a man's glorying before men, in a modest and humble manner, of what he is enabled to do, by the grace of God, without fetching in the characters of other men that are wicked, or have fallen, to illustrate his own.