Titus 1:16

They profess. Either Judaizing Christians or orthodox Jews, or both. Because of their emphasis upon intellectual speculations these unconverted teachers claim to know God, perhaps even better than the Christians. However, their behavior reveals their true master; they do not the works of God.

In works they deny. See on Matt. 7:21-27.

Being abominable. The insincere profession of these perverted religious teachers and “unruly” (v. 10) church members constitutes a great offense in the eyes of God. It would be better for such people if they had never heard of Christianity (see on Luke 12:47).

Reprobate. Gr. adokimos, “not standing the test,” “worthless” (see on 2 Tim. 3:8). As a result of their hypocritical, defiled, selfish lives, these men were useless for any good or noble work. Apparently many of the Cretan believers went to teachers of this kind for instruction in Christian doctrine and practice. Paul had no choice but to speak frankly concerning both the teachers and their followers.