Despite man's arrogant pride, he is utterly unable to save himself or to make himself acceptable to God. Neither is he able to keep himself saved nor, above all, is he able to defeat sin and conquer death.
But God is able! The word "able" (Greek dunamai) is closely related to the word for "power" (Greek dunamis), both speaking of God's spiritual dynamics. He is all powerful, His ability is without limit, and His power "works in us"!
Therefore, "he is able also to save them to the uttermost that come unto God by him" (Hebrews 7:25). Because the gospel of Christ is the "power of God unto salvation" (Romans 1:16), God "is of power to stablish you according to my gospel" (Romans 16:25).
Even when great troubles and sorrows and temptations come, He is able. "For in that he himself hath suffered being tempted, he is able to succour them that are tempted" (Hebrews 2:18). He "is able to keep you from falling, and to present you faultless before the presence of his glory with exceeding joy" (Jude 24).
In fact, He is able to meet every need of our lives and even to use us in His service. "God is able to make all grace abound toward you; that ye, always having all sufficiency in all things, may abound to every good work" (2 Corinthians 9:8).
Finally, "he is able to keep that which I have committed unto him against that day" (2 Timothy 1:12). That day will surely come, but then He will give us bodies of glory, for "he is able even to subdue all things unto himself" (Philippians 3:21). HMM