They profess that they know God; but in works they deny him, being abominable, and disobedient, and unto every good work reprobate.
All Commentaries on Titus 1:16 Go To Titus 1
Augustine of Hippo
All the heresies … they all say, “Jesus is Lord.” And he’s not, of course, going to eliminate from the kingdom of heaven those whom he finds to be in the Holy Spirit; and yet he did say, “Not everyone who says to me, Lord, Lord, will enter into the kingdom of heaven.” But: “Nobody can say: Jesus is Lord, except in the Holy Spirit”; nobody at all, evidently; but in the sense in which it was meant, that is in deeds…. The same apostle, you see, also says of some people, “They claim to know the Lord but deny it by their deeds.” As it can be denied by deeds, so it can be said by deeds.