Jamieson, Fausset and Brown on 1 Corinthians 3:20

20. Quotation from Psa 94:11. There it is of men; here it is "of the wise." Paul by inspiration states the class of men whose "thoughts" (or rather, "reasonings," as suits the Greek and the sense of the context) the Spirit designated in the Psalm, "vanity," namely, the "proud" (Psa 94:2) and worldly-wise, whom God in Psa 94:8 calls "fools," though they "boast themselves" of their wisdom in pushing their interests (Psa 94:4).