The Christian must have strength to serve the Lord and endure the hardships, temptations, and persecutions. However, this strength cannot come from the Christian himself. It must come from a greater source.
Strength must come from the Lord. "Finally, my brethren, be strong in the Lord and in the power of His might" (Eph. 6:10). When Paul prayed that his thorn in the flesh be removed, the Lord gave a response he was not expecting. "And He said to me, 'My grace is sufficient for you, for My strength is made perfect in weakness.' Therefore most gladly I will rather boast in my infirmities, that the power of Christ may rest upon me. Therefore I take pleasure in infirmities, in reproaches, in needs, in persecutions, in distresses, for Christ's sake. For when I am weak, then I am strong" (2 Cor. 12:9-10).
Strength comes from His word. God's word is our source of spiritual nourishment. "As newborn babes, desire the pure milk of the word, that you may grow thereby" (1 Pet. 2:2). "So now, brethren, I commend you to God and to the word of His grace, which is able to build you up and give you an inheritance among all those who are sanctified" (Acts 20:32).
Strength is found in prayer. Samson regained his strength when he prayed unto God (Judges 16:28). We are the strongest when we are on our knees before the throne of God, seeking His will and His help in our lives.
Strength comes from fellowship with God's people. God has united His people together in one body (the church) through Christ. This is an incredible source of strength. "And let us consider one another in order to stir up love and good works, not forsaking the assembling of ourselves together, as is the manner of some, but exhorting one another..." (Heb. 10:24-25).