John Calvin Commentary 1 Corinthians 1:31

"that, according as it is written, He that glorieth, let him glory in the Lord." — 1 Corinthians 1:31 (ASV)

He that glorieth let him glory in the Lord. Notice the purpose God has in view in bestowing all things upon us in Christ—that we may not claim any merit for ourselves, but may give him all the praise. For God does not strip us with the intention of leaving us bare, but immediately clothes us with his glory—yet on this condition, that whenever we glory, we must go out of ourselves.

In short, man, brought to nothing in his own estimation, and acknowledging that there is nothing good anywhere but in God alone, must renounce all desire for his own glory, and with all his might aspire to and aim at the glory of God exclusively. This is also more clearly apparent from the context in the writings of the Prophet, from whom Paul borrowed this testimony. For in that passage the Lord, after stripping all mankind of glory regarding strength, wisdom, and riches, commands us to glory only in knowing him (Jeremiah 9:23–24). Now he would have us know him in such a way as to know that it is he that exercises judgment, righteousness, and mercy. For this knowledge produces in us simultaneously confidence in him and fear of him.

If, therefore, a man has his mind regulated in such a way that, claiming no merit for himself, he desires that God alone be exalted; if he rests with satisfaction on his grace, and places his entire happiness in his fatherly love; and, finally, is satisfied with God alone, that man truly glories in the Lord. I say truly, because even hypocrites on false grounds glory in him, as Paul declares (Romans 2:17), when, being either puffed up with his gifts, or elated with a base confidence in the flesh, or abusing his word, they nevertheless take his name upon themselves.