This amazing assurance of God's unlimited ability to answer our prayers is related to a unique "power [Greek dunamis] that worketh in us." Paul had used the same word twice before in this same epistle, speaking of "the exceeding greatness of his power to us-ward who believe," and "the gift of the grace of God given unto me by the effectual working of his power" (Ephesians 1:19; 3:7). "Effectual working" in the original is one word, energeia, from which we get our word "energy."
Such power working in us is actually nothing less than the presence of God Himself. Its very first occurrence is in the model prayer. "For thine is the kingdom, and the power, and the glory, for ever" (Matthew 6:13). It is this "power of God unto salvation" which is received when we first believe on Christ through the gospel (Romans 1:16). It has been so ever since the fulfillment of Christ's promise when He told His disciples that "ye shall receive power, after that the Holy Ghost is come upon you" (Acts 1:8).
This remarkable power of God is thus imparted to us and energized in us by the Holy Spirit. Because of this, we can be filled "with all joy and peace in believing, that ye may abound in hope, through the power of the Holy Ghost" (Romans 15:13). Furthermore, He thereby provides impregnable security for time and eternity, for we "are kept by the power of God through faith unto salvation ready to be revealed in the last time" (1 Peter 1:5).
With such a resource of unlimited spiritual power working in us, God is able indeed to accomplish far more than we can ever imagine, as He works in and through those yielded to His will. HMM