“Finally, my brethren, be strong in the Lord, and in the power of His might” (Eph. 6:10).
As Paul begins to close the letter to the Ephesians, he addresses the spiritual warfare of the Body of Christ. Paul’s instruction is for us to “be strong in the Lord, and in the power of His might.” In this spiritual battle, we need spiritual strength. As we are on the Lord’s side, Paul points us to the Lord Almighty, from Whom we are to get our strength. In this epistle, Paul has been showing believers that we are “in Christ,” in perfect, eternal union with Him. Being in Christ, we find that His life is our life and His power is our power. We, the Body, draw the strength and power for living the Christian life from our living Head.
“What is the exceeding greatness of His power to us-ward who believe, according to the working of His mighty power, which He wrought in Christ, when He raised Him from the dead…” (Eph. 1:19,20).
Being strong in the Lord and in the power of His might has to do with living by faith in the resurrection life and power which resides in every believer through Christ. The same power that raised Christ from the dead is the same power we’re to use to stand in this spiritual battle. The strength of the Christian life is dependence on God. So Paul points the Church to be “strong in the Lord,” to depend upon Him.
Before salvation, Paul says we are “without strength” (Rom. 5:6). We are weak and absolutely unable to please God or save ourselves. Salvation is only through trusting Christ, and by Him alone we have victory over sin’s penalty and punishment. After trusting Christ as our Savior, we are still weak in ourselves, and in the Christian life our sufficiency must be of God (II Cor. 3:5). Victory over sin’s power in our lives occurs the same way we are saved from sin’s penalty, by wholly trusting Christ and Him alone. His strength is more than sufficient for the battle, and we are guaranteed victory over anything Satan throws at us when we turn to our Lord (Phil. 4:13). source