For the rest, brethren, be strong in [the] Lord, and in the might of his strength.
The letter has just told ordinary people how to live at home and at work. Now it changes tone: before it names a single enemy, it calls them to be strong in the Lord.
The order of the call
Commentators notice what the verse does not do. It does not open by sizing up the enemy.
"Finally, be strong in the Lord and in the strength of his might." This is like the first sound of a trumpet. To what does it call the saints — does it call you? Not to survey the enemy's stronghold, or to show you what you have to overcome, but to turn all your thoughts gently to the Lord Himself. Before it says a word about enemies or conflicts, it calls you to survey your strength. That strength is the mighty Lord, seated at the right hand of God in the heavenly places.
Nothing of our own
The hard part of this command is what you have to admit. We would rather be strong in something we can count.
The Apostle points our thoughts to the power that is for us. Only then does he describe the power against us. To face this conflict we must always remember that all our strength is in the Lord. Our difficulty is often to realise that we have no strength in ourselves. We would like to be strong in numbers, strong in gifts, or strong in the power of some forceful leader. But our real and only strength is "in the Lord and in the strength of His might".
Weakness, then, is not the obstacle. It is the doorway — and the foe we face has already lost to the One we lean on.
The word "Finally" (older translations read "Finally, my brothers") shows that what we have considered leads up to this climax. On our own we are no match for the enemy. But the Lord has met him and overcome him. If we are strong in Him, our very weakness makes room for the one power that can defeat him. He showed the might of His strength when He went down into the enemy's territory, overcame him, and led a host of captives. We have to meet a foe whose power the Lord has broken, but who still tries to overcome us by his tricks.
What "in the Lord" asks of us
The title used here is "the Lord" — the One with authority. That shapes what the command asks of us.
"Be strong in the Lord" means: be wholly subject to the Lord's authority. That subjection is true strength. It opens to us the power of His might — an inward, living strength that evil cannot overcome, even when we look weak.
The size of the power offered
The strength named in the verse is not vague. Earlier in the same letter the writer had already measured it, and the comparison is the point.
The prayer of the first chapter brings before us the power of God's might. God has raised Christ from the dead and set Him at His own right hand in heavenly places, "far above all rule and authority and power and dominion, and above every name that is named, not only in this age but also in the one to come". Now, says the Apostle, that is the "immeasurable greatness of His power toward us who believe". The power against us is far greater than our own. But the power toward us surpasses every power that opposes us.
How the strengthening happens
The verb itself suggests something received rather than worked up.
The real idea here is a passive one. "Be strengthened in the Lord." There can be no real difficulty in understanding this. Who has not talked over their troubles with a friend, and come away stronger for the sympathy and advice? It is far more true of the Lord. When we keep coming to Him, His power flows into us — power greater than anything that can stand against us in the spiritual battle.
What the fight is over
We need this strength for something specific: holding on to what already belongs to us.
All our blessings are in the heavenly places in Christ. Satan and his angels are still there, so we have to fight for every bit of ground we hold... God gave the whole land of promise to Israel... But they had to fight for every inch of it to hold it in practice. So the heavenly places are ours — but how much have we laid hold of?
Summary
- Look up first. The call turns your eyes to the Lord before it mentions the enemy. Survey your strength, not the enemy's stronghold.
- Own your weakness. Numbers, gifts and strong leaders are not the strength meant here. Admitting you have none of your own makes room for the only power that defeats the foe.
- Submit, and be strengthened. Being subject to the Lord's authority is itself strength. You receive that strength by coming to Him again and again, and His power flows in.
- Measure the power. It is the same might that raised Christ and set Him far above every rule and authority. That power surpasses everything against us.
- Hold the ground. The blessings in heavenly places are already ours; the fight is over how much of them we take hold of.