What does it mean to be strong in the Lord in Ephesians 6:10?

from the old testament

• When God commissioned Joshua, He told him to be strong and courageous, saying, "Be strong and very courageous. Be careful to obey all the law my servant Moses gave you; do not turn from it to the right or to the left, that you may be successful wherever you go" (Joshua 1:7, NIV). This strength would come as Joshua meditated on and did everything according to the Word of God (the Law) for strength, as stated in Joshua 1:8: "Keep this Book of the Law always on your lips; meditate on it day and night, so that you may be careful to do everything written in it" (NIV). In turn, God promised him that He would always be with him as he led the children of Israel into the Promised Land (Joshua 1:6–9).
• Psalm 27:14 encourages us to be strong and take heart, waiting for the Lord with patient trust. It highlights that strength comes from relying on God’s timing and faithfulness, even in times of uncertainty.

from the new testament

• Ephesians 6:10–20 discusses the armor of God. Verse 12 draws our attention to the reality of the spiritual warfare going on around us. The command to "be strong in the Lord" has to do with living a spiritually victorious life. This relates to standing firm in the faith, to persevering in trust in God, to putting sin in our lives to death, and to resisting our enemy Satan (1 Corinthians 16:13; Hebrews 3:12–14; 1 Peter 5:6–9).
• In Ephesians 1:3–14, Paul explains some of the advantages of being in Christ. We are blessed with "every spiritual blessing in the heavenly places" (Ephesians 1:3), chosen "that we should be holy and blameless" (Ephesians 1:4), adopted (Ephesians 1:5), redeemed (Ephesians 1:7), and forgiven (Ephesians 1:7). God's grace is described as having riches and being "lavished upon us, in all wisdom and insight" (Ephesians 1:8). We have an inheritance (v. 11) and have received the Holy Spirit as a guarantee of it (Ephesians 1:13–14). These spiritual blessings strengthen us in the Lord.
• Paul reminds us of what God said to him when he was upset by his own human weakness: "But he said to me, 'My grace is sufficient for you, for my power is made perfect in weakness.' Therefore I will boast all the more gladly of my weaknesses, so that the power of Christ may rest upon me. For the sake of Christ, then, I am content with weaknesses, insults, hardships, persecutions, and calamities. For when I am weak, then I am strong" (2 Corinthians 12:9–10). In Paul's personal weakness, he found his strength, power, and contentment in God.
• Through God's strength, we can do all that He calls us to do (Philippians 4:12–13; 2 Peter 1:3).
• Paul describes "the immeasurable greatness of his power toward us who believe;” it is this same power by which Jesus rose from the dead. Certainly God has plenty of strength for us (Ephesians 1:19)!
• As we put on the armor of God, we begin to walk in His strength, rather than in our own (Ephesians 6:10–18). This spiritual armor is given to us by His grace but is also an act of our will to put it on. If we neglect to “put on” truth and righteousness (Ephesians 6:14), or neglect to prepare ourselves with the gospel (Ephesians 6:15), or take up our shield of faith (Ephesians 6:16), we will not be strong. If we don’t carry the Word of God in our hearts and pray (Ephesians 6:17–18) we will not be able to stand against the evil one.

implications for today

While it sounds simple to rely on someone else for strength and while we know that God is eminently capable of strengthening us, living it out in practice can be a bit challenging. Not many of us relish reliance on others. Not many of us readily see and admit our needs and weaknesses. But when we attempt to stubbornly cling to our own strength and desire for total self-sufficiency, we will inevitably find ourselves and our resources lacking. When we trust in the Lord, we will be strengthened. We can receive His provision—whether directly from the Holy Spirit, through His Word, through the ways He gives us one another for mutual encouragement and edification, or any other way in which He strengthens us—with gratitude. In relying on God, we do not become progressively weaker, but actually progressively stronger and more able to live according to His good design. When we rely on God, He is our source of strength, and His stores are infinite.

Ephesians 6:10–18 helps us see some of the ways we are strengthened in the Lord: He helps us to stand against the schemes of the devil and withstand in the evil day, standing firm. He helps us extinguish all the flaming darts (attacks) of the evil one. The armor of God makes us strong in Him: truth, righteousness, readiness to proclaim the gospel of peace, faith, salvation, the Word of God, and praying in the Spirit strengthens us in the Lord against the enemy, the flesh, and the fleeting, empty desires of this world. As we put on the armor of God, we begin to walk in His strength, rather than in our own. We are strengthened by Him, made strong in Him. With God as our strength, we will not falter, and we will be able to persevere in living for Him throughout the triumphs and hardships alike that we face (see Psalm 18:29–36).