Jamieson, Fausset and Brown on 2 Timothy 3:9

9. they shall proceed no further--Though for a time (2Ti 2:16) "they shall advance or proceed (English Version, 'increase') unto more ungodliness," yet there is a final limit beyond which they shall not be able to "proceed further" (Job 38:11; Re 11:7, 11). They themselves shall "wax worse and worse" (2Ti 3:13), but they shall at last be for ever prevented from seducing others. "Often malice proceeds deeper down, when it cannot extend itself" [Bengel].

their folly--literally, "dementation": wise though they think themselves.

shall be manifest--Greek, "shall be brought forth from concealment into open day" [Bengel], (1Co 4:5).

as theirs ... was--as that of those magicians was, when not only could they no longer try to rival Moses in sending boils, but the boils fell upon themselves: so as to the lice (Ex 8:18; 9:11).