{Let no man deceive himself} (M(8864)eis heauton exapat(935c)). A
warning that implied that some of them were guilty of doing it
(m(885c) and the present imperative). Excited partisans can easily
excite themselves to a pious phrenzy, hypnotize themselves with
their own supposed devotion to truth. {Thinketh that he is wise}
(dokei sophos einai). Condition of first class and assumed to
be true. Predicate nominative sophos with the infinitive to
agree with subject of dokei (Robertson, _Grammar_, p. 1038).
Paul claimed to be "wise" himself in verse  10  and he desires
that the claimant to wisdom may become wise (hina gen(8874)ai
sophos, purpose clause with hina and subjunctive) by becoming
a fool (m(9372)os genesth(935c), second aorist middle imperative of
ginomai) as this age looks at him. This false wisdom of the
world ( 1:18-20,23  2:14 ), this self-conceit, has led to strife
and wrangling. Cut it out.