I think we can determine that by looking at the context:Titus 1
10For there are many unruly and vain talkers and deceivers, specially they of the circumcision: 11Whose mouths must be stopped, who subvert whole houses, teaching things which they ought not, for filthy lucre's sake. 12One of themselves, even a prophet of their own, said, The Cretians are alway liars, evil beasts, slow bellies. 13This witness is true. Wherefore rebuke them sharply, that they may be sound in the faith; 14Not giving heed to Jewish fables, and commandments of men, that turn from the truth. 15Unto the pure all things are pure: but unto them that are defiled and unbelieving is nothing pure; but even their mind and conscience is defiled. 16They profess that they know God; but in works they deny him, being abominable, and disobedient, and unto every good work reprobate.
They profess to know God but in works they deny him. Being DISOBEDIENT.
"And these are his commandments, believe in Jesus and love thy neighbor." So simple.
Paul said. I do that which I desire not?
If you look at the context it shows that this was only true when he attempted to attain righteousness UNDER THE LAW
. Paul always taught us not to do that, and if we do, we are fallen from grace which according to him in Titus 2: "grace that brings salvation has appeared to all men, TEACHING (paiduo - chastening) us to deny ungodliness and live sober lives in this present age."
...what if ...in works they deny Him..means this.......they go back to salvation of works by the law?
If they go back to the Law, "the motions of sin"
will reassert themselves.Romans 7
12 So then, the law is holy, and the commandment is holy, righteous and good. 13 Did that which is good, then, become death to me? By no means! Nevertheless, in order that sin might be recognized as sin, it used what is good to bring about my death, so that through the commandment sin might become utterly sinful.
The motions of sin by the Law. Sin taking advantage by the commandment to become exceeding sinful, so that sin be recognized as sin. Grace comes to deliver us from sin. So, if they go back to the Law, they will naturally become, as Paul said "unto every good work, reprobate."