As in Hebrews 3, Jude takes the tone of warning and exhortation in Jude 5-7 to admonish believers to remember how God had judged past unbelief. As believers we must regularly exhort one another so that we are not taken captive by disbelief or deception. Contending for the faith is not only an offensive stance. It is defensive. All sin is rooted in disbelief, so we must contend to abandon disbelief before we abandon God.