"...know that the LORD hath set apart him that is godly for himself..." (Psalm 4:3)
Jude 20:21, "But ye, beloved, building up your selves on your most holy faith, praying in the Holy Ghost.  Keep yourselves in the love of God, looking for the mercy of our Lord Jesus Christ unto eternal life."
I'm glad I am saved and can live life with the expectation of enjoying eternal life and the mercy of our Lord Jesus Christ. Jude in today's passage speaks about three things the believer should be careful to do:
1. Build yourself up in the faith. Faith in this verse speaks of the sphere of what we believe. We need to be students of the Bible and take what we read and learn and build a faith walk with the Lord.
Maintain a spiritual prayer life. "Praying in the Holy Ghost." Most of the prayers of our day are prayers about personal comfort. We need to be praying about spiritual victories, i.e. revival, salvation decisions, Holy Spirit power, growth in discipleship etc. Let's learn to pray in the Holy Ghost.
Keeping yourself in the love of God. It is impossible for any person to not be loved by God, therefore, I believe this verse is speaking about our remaining constant based upon God's love for us. Keeping in view the love of God for us will bring us to the place of faithful service to Him. Jesus said, "If ye love me, keep my commandments." (John 14:15) Keeping ourselves in the love of God should lead to obedience.
May we live daily in such a manner as to expect to know and realize the mercy of God and be blessed knowing we have eternal life.