Titus 1:15-16
15 Unto 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.
16 They profess that they know God; but in works they deny him, being abominable, and disobedient, and unto every good work reprobate.
The Grace New Testament Commentary - Titus 1:15-16
1:15-16 Paul concludes his warning about the false teachers by condemning their character and conduct. For these men nothing is pure. They are defiled and unbelieving (apistos). The latter could better be translated unfaithful. The word faithful (pistos) is used three times in this epistle (Titus 1:6, 9; 3:8). Whether these men are believers or unbelievers, the issue here is their unfaithfulness, not their standing as regenerate or unregenerate.
This defilement has damaged both their mind and conscience. They do not think Biblically. They lack the mind of Christ (1 Cor 2:16). Their conscience is such that sinful actions do not cause them discomfort.
"They profess to know God, but in works they deny Him". This statement and the words that follow it lead many to conclude that these men were unregenerate. However, their profession here is that they knew God in their experience. Yet their works show they did not know him in their experience. These men are abominable, disobedient, and disqualified for every good work. Abominable (bdelktos, used only here in the NT) could also be translated detestable, repugnant, or abhorrent. They are not obedient (apeitheis) to God, and thus in regard to every good work (Greek word order) they are disqualified (adokimos, last in the Greek sentence for emphasis). Adokimos and its antonym dokimos are used elsewhere in the NT of believers who are disapproved or approved by God or men (Rom 1:28; 14:18; 16:10: 1 Cor 9:27; 11:19: 2 Cor 10:18; 13:5-7: 2 Tim 2:15; 3:8; Heb 6:8; James 1:12). However, while disobedient believers are disapproved, so of course are all unbelievers. Thus it is not clear whether these disgusting false teachers were all unbelievers or not. However, they were repugnant and were to be opposed.