Albert Barnes Commentary 2 Timothy 2:17

"and their word will eat as doth a gangrene: or whom is Hymenaeus an Philetus;" — 2 Timothy 2:17 (ASV)

And their word. The word, or the discourses of those who love vain and idle disputations.

Will eat as does a canker. A marginal note suggests gangrene. This word, gaggraina, occurs nowhere else in the New Testament. It is derived from graiw, grainw, graio, or graino—meaning to devour or corrode—and signifies gangrene or mortifications: the death of a part of the body, which, unless arrested, gradually spreads over the whole. The phrase translated as "will eat" means it will find nourishment; that is, it will spread over and consume the healthy parts. It will not merely destroy the parts immediately affected, but will also extend into the surrounding healthy parts and destroy them.

So it is with erroneous doctrines. They will not merely eat out the truth in the particular matter to which they refer, but they will also spread over and corrupt other truths. The doctrines of religion are closely connected and dependent on each other—like the different parts of the human body. One part cannot be corrupted without affecting those adjacent to it, and unless checked, the corruption will soon spread over the whole.

Of whom is Hymeneus and Philetus. Regarding Hymeneus, see the comments on 1 Timothy 1:20.

Nothing more is known of Philetus. They have gained an undesirable immortality, destined to be known until the end of time only as the advocates of error.