From the day of our conversion we are involved in spiritual warfare. The enemy of souls, Satan, our adversary, will attack us at every opportunity.
The command, ‘Be strong’, in Greek is in the passive voice. In other words, it might be better to translate it, be strengthened, be enable. This is not something to your credit; this is something to help you in your weakness. ‘Finally, my brethren, be enabled, be strengthened,’ that's what we need, ‘in the Lord’, and that has two senses. First of all, all our success is due to him. Do I have spiritual life? Yes, by conversion, by salvation. Who secured it? Christ the Lord did. He suffered and died to bare my sin. He lived a perfect life of righteousness under tremendous provocation to deserve heaven and blessing and acceptance with God for me. So I am saved in his strength, not mine. That ties in. ‘Be enabled’ – it is something he does. In everything he will do it. If the enemy attacks me, for example, with a deep doubt – ‘You cannot be a believer. You cannot be truly converted. You cannot be the Lord's because you just sinned.’ Now this does not encourage us to complacency, but he may attack along these lines. ‘You just sinned, therefore you must be lost. You cannot be saved. You cannot be one of his.’ Then we remember that we are strong in the Lord. He has covered our sin. He has suffered in our place. He has taken our punishment. He has earned our acceptance with God. I stand not according to my weakness, but according to his saving power.
But it works in a second sense too. If he has all power, then he can certainly help me in anything. Think of Christ, he created all things from nothing. He was the member of the Godhead to whom was deputed the task of the creation of the universe according to the Scripture, and he at a word brought everything into being. If he can create all things out of nothing, surely he can make me a better person. If I pray to him for help, he can renew my whole being, he can subdue whatever it is, my lust, my temper and enable me and help me. If he suffered and died and rose from the dead, he can give me life when I am spiritually cold and I have foolishly turned aside and lost my sense of his love and his nearness. So this is the exhortation, ‘Be strong in the Lord,’ seek help from him, ‘and in the power of his [eternal] might.’ He has all the resources.