vv. 20-21 But you, beloved, build yourselves up on your most holy faith; pray in the Holy Spirit; keep yourselves in the love of God; look forward to the mercy of our Lord Jesus Christ that leads to eternal life.
The Epistle of Jude claims to have been written by one of Jesus' brothers, which would also have made him a brother of James of Jerusalem, the leader of the church their after Jesus' departure. It is not clear at all to whom this short letter is written. The community, however, is clearly experiencing conflict over some rival teaching that has come into it. Paul seems to have run into this teaching as well, which basically held that since grace has saved us, we are free to do whatever we want. Jude vigorously denounces this philosophy.
The two verses quoted above are Jude's simple outline for following the Christian faith. Depend on your faith (and by this he would have meant the faith handed down to you from the apostles). Pray, listening for the Spirit (and not your own voice, which could lead you astray). Rest assured of God's love. Look forward, trusting ever in the mercy of Jesus that will lead you to eternal life. It's not a bad outline at all.
Our outline along these lines is the Baptismal Covenant: Continue in what the apostles taught us and told us to do. Keep turning back to God whenever you stray away. Proclaim that relationship with God in Christ is good news. Look to serve Christ in all people, which is what it means to love your neighbor as yourself. Keep the struggle for justice, peace and the dignity of all people alive.
This is the faith of the babe to be born. This is what it means for the incarnation of God to continue in his people, you and me.