He must hold firmly to the trustworthy word [of God] as it was taught to him, so that he will be able both to give accurate instruction in sound [reliable, error-free] doctrine and to refute those who contradict [it by explaining their error].

This description is true. So rebuke them sharply so that they will be sound in the faith and free from doctrinal error,

For we were once ourselves also without intelligence, disobedient, wandering in error, serving various lusts and pleasures, living in malice and envy, hateful, and hating one another.

Clearly he is in error and a sinner, being self-judged.