"But you, dear friends, by building yourselves up in your most holy faith and praying in the Holy Spirit, keep yourselves in God’s love as you wait for the mercy of our Lord Jesus Christ to bring you to eternal life."

Jude 1:20-21

Jude gives some pointers: apostates are contemptuous about truth and purity (v. 18); they’re led by their ungodly desires, fanciful dreams (v. 8, and natural instincts (v. 19); they bring division (v. 19). They do not have the Spirit of God in them and do not produce the fruit of the Spirit—we must recognize this and have nothing to do with it.

Always remembering that God loved us while we were yet sinners, we must build on the foundation of our most holy faith, praying in the strength and wisdom of his Spirit. We are to keep ourselves in God’s love for us, experiencing its benefits and looking forward with hope to Jesus’ mercy in keeping his promises vv. 20,21).

While Jude has emphasized our responsibilities as believers, he concludes by reminding us of God’s faithfulness that is always at work in us. No matter what are our sins, shortcomings, or failures, his power is able to keep us from falling and to present us blameless.

24-25 "To him who is able to keep you from stumbling and to present you before his glorious presence without fault and with great joy— 25 to the only God our Savior be glory, majesty, power and authority, through Jesus Christ our Lord, before all ages, now and forevermore! Amen." (edited from Encounter with God).