It instructs us: The emphasis of this instruction falls on the positive virtues: wisdom, righteousness, and devotion to God. In Greco-Roman writings, these three virtues represent virtuous behavior in general. These virtues counter the Cretan vices (immoral behaviors or qualities) listed in 1:12 and are transformed into thoroughly Christian qualities (see 2:13).
Paul encourages the Cretans to embody these virtues, in order to clearly show their fellow Cretans that a virtuous life comes only from God’s grace in Jesus Christ.