These things speak and exhort and reprove with all authority. Let no one disregard you. (Titus 2:15)
Preach
For those who have never heard, this doctrine is designed to teach and train them.
Comfort
For those who have heard and believe, these words are to be a comfort.
Admonish
For those who have heard and do not believe, these words are to be a sharp rebuke.
Titus is to deliver these words with the authority that comes from God alone. It is the same authority by which Jesus sent out the apostles (Matthew 28) and it is the same authority granted to believers today. And because the authority is given to us by God himself, we are to let no one ignore or despise these teachings.