Assured of his eternal Heavenly salvation - "I know whom I have believed, and am persuaded that He is able to keep that which I've committed to Him against that day" - the Apostle Paul could not be certain that a lifetime of earthly faithfulness would characterize his walk with God - "I keep under my body, and bring it into subjection: lest that by any means, when I have preached to others, I myself should be a castaway" (II Timothy1:12; I Corinthians 9:27).
The Lord Jesus Christ faithfully secured Paul in His redeemed flock, as He does all who receive His free gift of eternal life. God charged Paul, however, with keeping his body under submission, that is, the Lord called the Apostle to serve as steward of his humanity by consistently remembering, affirming, and acting upon the truth that his body belonged not to himself, but to his God. The same mandate of determined participation in a faithful earthly life also applies to all believers.
"Blessed be the God and Father of our Lord Jesus Christ, which according to His abundant mercy hath begotten us again unto a lively hope by the resurrection of Jesus Christ from the dead, to an inheritance incorruptible, and undefiled, and that fadeth not away, reserved in heaven for you, who are kept by the power of God through faith unto salvation ready to be revealed in the last time" (I Peter 1:3-5).
"I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service" (Romans 12:1).
Thankfully, we know that Paul did in fact finish his course, remaining faithful to the end through the power of the Spirit of Christ (II Timothy 4:7-8). As was the case with our brother of old, however, we do not know that we ourselves will join him in a lifetime of faithfulness. We can be sure of a salvation kept by Christ, again, as Paul knew. Our application of such grace during our earthly lifetime, however, remains a daily adventure and challenge. Our spiritual enemies seek to discourage and sidetrack us. They possess the means to do so. They cannot take our salvation from us, because to do would require them to somehow prevent the securing work of our heavenly High Priest, who "ever liveth to make intercession for us" (Hebrews7:25). Our enemies can, however, sidetrack the present life of faithfulness to which our Heavenly Father calls us. "Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour" (I Peter 5:8).
A relationship kept by God makes possible an ongoing fellowship and faithfulness with God. The relationship is sure. The experience of fellowship and faithfulness is not. We wouldn't want it any other way. Indeed, if salvation required our efforts to access and maintain, no human being could attain the perfection required. Conversely, if the living of the Christian life did not require our passionate participation and trusting submission to God, no human being would find relationship with the Lord Jesus meaningful or real. Our Heavenly Father constituted us as persons rather than robots or computers. No mere programmed machine could glorify Him in the manner believers accomplish, as led and enabled by the Holy Spirit. Nor could we truly experience life apart from the vital freedom whereby love is real, choices matter, and consequences, whether positive or negative, always ensue from our innermost determinations. "I will love Thee, o Lord my strength" declared the Psalmist who well knew the necessity of both his "I will," and God's "strength" (Psalm18:1). We must know the same, rejoicing in the gift of being kept by our Savior. Upon the basis of such mercy, we then devote ourselves to keeping under submission our human capacities and faculties by deliberately availing ourselves of God's abiding presence and power. We are kept, as it were, in order to keep. Indeed, a growing understanding of "kept" makes possible and actual a growing experience of "keep."
"Now unto Him that is able to keep you from falling, and to present you faultless before the presence of His glory with exceeding joy, to the only wise God our Savior, be glory and majesty, dominion and power, both now and ever. Amen."(Jude 1:24-25)
"Keep yourselves in the love of God, looking for the mercy of our Lord Jesus Christ unto eternal life."(Jude 1:21)