They profess that they know God; but in works they deny him, being abominable, and disobedient, and unto every good work reprobate.
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Augustine of Hippo
AD 430
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.
"For who of those who are wise would not choose to reign in God, and even to serve? So some "confess that they know God "according to the apostle; "but in works they deny Him, being abominable and disobedient, and to every good work reprobate."
They confess that they know God. He speaks not therefore of those who were properly infidels, without the knowledge of the true God; so that it is foolish to pretend from hence, that every action of an infidel must be a sin. (Witham)
Some think that this verse applies only to those who deny the faith during a persecution, but the apostle contends that all perverse behavior denies God. .
But he that has a weak soul makes everything unclean, and if there be set abroad a scrupulous inquiry into what is clean or unclean, he will touch nothing…. Yet Paul says not so; he turns the whole matter upon themselves. For nothing is unclean, he says, but themselves, their mind and their conscience; and nothing is more unclean than these; but an evil will is unclean.
The swine therefore is clean. Why then was it forbidden as unclean? It was not unclean by nature; for, all things are pure. Nothing is more unclean than a fish, inasmuch as it even feeds upon human flesh. But it was permitted and considered clean. Nothing is more unclean than a bird, for it eats worms; or than a stag, which is said to have its name from eating serpents. Yet all these were eaten. Why then was the swine forbidden, and many other things? Not because they were unclean, but to check excessive luxury. But had this been said, they would not have been persuaded; they were restrained therefore by the fear of uncleanness. For tell me, if we enquire nicely into these things, what is more unclean than wine; or than water, with which they mostly purified themselves? They touched not the dead, and yet they were cleansed by the dead, for the victim was dead, and with that they were cleansed. This therefore was a doctrine for children. In the composition of wine, does not dung form a ...
Our peace also has its dangers, dearly beloved. In vain do people feel secure as a result of freedom for their faith if they do not resist the desires of vice. By the quality of works is the human heart made known, and outward actions disclose the beauty of souls. There are some, as the apostle says, who “profess to know God but deny him through their deeds.” Truly the guilt of denial is incurred when the ears have heard what is good but the conscience does not hold on to it. The frailty of the human condition easily slides into sin.