Jamieson, Fausset and Brown on 2 Timothy 2:18

18. erred--Greek, "missed the aim" (see 1Ti 6:21).

is past already--has already taken place. The beginnings of the subsequent Gnostic heresy already existed. They "wrested" (2Pe 3:16) Paul's own words (Ro 6:4; Ep 2:6; Col 2:12) "to their own destruction," as though the resurrection was merely the spiritual raising of souls from the death of sin. Compare 1Co 15:12, where he shows all our hopes of future glory rest on the literal reality of the resurrection. To believe it past (as the Seleucians or Hermians did, according to Augustine [Epistles, 119.55, To Januarius, 4]), is to deny it in its true sense.

overthrow--trying to subvert "the foundation" on which alone faith can rest secure (2Ti 2:19; compare Tit 1:11).