My confidence is not in my election, my confidence is in Christ Jesus.
There is a clear and crucial distinction between the security and assurance of one's salvation. The former is an objective fact grounded in the work of Christ applied by the Spirit, while the latter is a subjective experience grounded in the word of Christ affected by the Spirit.
The doctrine that teaches the eternal security of our salvation finds its basis in the love and grace of God who reconciled believers with himself for his own glory through the redemption accomplished by Jesus Christ and for his sake. This great salvation is all of grace; it does not depend on anything we say or do but wholly upon the sinless Son of God. As such, it cannot be placed in jeopardy by anything we say or do. Any teaching that claims a person can lose his salvation ends up making salvation conditional on human merit, attributing in part to man what wholly belongs only to Christ. If salvation is not secured by any merit of ours, then neither is it jeopardized by any demerit of ours. Salvation belongs to the Lord (Jonah 2:9; Ps. 3:8; 68:20; Acts 4:12; Rev. 7:10).
Moreover, the security of our salvation is not a matter of our possessing assurance thereof. In other words, our salvation rests upon the perfect and finished work of the Son of God, not what our transient feelings happen to be telling us at any given moment. What is happening in such cases is that we are looking at ourselves in search of assurance, when the proper ground of assurance should be the same as that of security: Jesus Christ. Peter confidently walked on water so long as he remained focused on Christ; but when he took his eyes off Christ and looked to himself, that is when he doubted and sank below the waves.
The work of Christ grounds our security and the word of Christ grounds our assurance (the word of Christ being the gospel of God's promises). We do not look to our faith for assurance of our salvation but to Christ alone, for Benjamin Warfield was right when he observed: It is not faith in Christ that saves, but Christ who saves through faith. When your faith is at its weakest, Christ remains the sure and solid Rock of your salvation. Rest in him, and him alone.