There are three wonderful doxologies in three New Testament epistles extolling the transcendent ability of God to accomplish and perfect our eternal salvation. One is our text above, assuring all who are "looking for the mercy of our Lord Jesus Christ unto eternal life" (Jude 21) that He is fully able to bring us joyfully into the presence of God in glory.
Then, look at Ephesians 3:20: "Now unto him that is able to do exceeding abundantly above all that we ask or think, according to the power that worketh in us." Furthermore, His power is able to keep us forever. "Now to him that is of power to stablish you according to my gospel, and the preaching of Jesus Christ, according to the revelation of the mystery, which was kept secret since the world began" (Romans 16:25).
Little wonder that the apostles exhort us to praise such a wonderful God and Savior! But in addition to the three doxologies, the Word of God contains many other testimonies to the omnipotent ability of the Lord on behalf of His people. "He is able to keep that which I have committed unto him against that day" (2 Timothy 1:12). "He is able also to save them to the uttermost that come unto God by him, seeing he ever liveth to make intercession for them" (Hebrews 7:25). "The Lord Jesus Christ: . . . shall change our vile body, that it may be fashioned like unto his glorious body, according to the working whereby he is able even to subdue all things unto himself" (Philippians 3:20-21).
With such a Savior and heavenly Father, we can join with Jude as he concludes his doxology: "To the only wise God our Saviour, be glory and majesty, dominion and power, both now and ever. Amen" (Jude 25). HMM http://www.icr.org/articles/type/6/