Having a form of godliness - That is, they profess religion, or are in connection with the church. This shows that the apostle referred to some great corruption in the church; and there can be little doubt that he had his eye on the same great apostasy to which he refers in 2 Thessalonians 2:, and 1 Timothy 4: All these things to which he refers here have been practiced and tolerated in that apostate church, while no body of men, at any time, have been more zealous in maintaining “a form of godliness;” that is, in keeping up the forms of religion.
But denying the power thereof - Opposing the real power of religion; not allowing it to exert any influence in their lives. It imposes no restraint on their passions and carnal propensities, but in all respects, except in the form of religion, they live as if they had None. This has been common in the world. The most regular and bigoted adherence to the forms of religion furnishes no evidence in itself that there is any true piety at heart, or that true religion has any actual control over the soul. It is much easier for people to observe the forms of religion than it is to bring the heart under its controlling influence.
From such turn away - Have no contact with them as if they were Christians; show no countenance to their religion; do not associate with them; compare 2 John 1:10-11; see the notes at 2 Corinthians 6:17.