Main point summary
Be strong in the Lord and His strength by putting on the armor He provides so that you will be able to stand firm in the war against the devil.
We are in a battle, a spiritual battle that necessitates us relying on God's strength and the armor he provides. Why must we wear God's armor? We are at war, not with enemies of our own nature and being, but with enemies of "this present darkness." The enemies we are at war with are ones we once held allegiance to when we were "dead in [our] trespasses and sins" (Eph. 2:1). We cannot expect to fight them on our own. This passage is one of action. It says to "be strong," to "stand firm," to "put on" God's armor. We mustn't forget that all of this comes from Jesus. All of this strength, all of this standing firm is done "in the strength of his might." In verse 18, to what "end" or purpose is Paul referring to? To the purpose of standing firm, or to the purpose of "praying at all times in the Spirit"? It seems that there is a focus on prayer for our brothers and sisters in the Lord: with prayer we can appeal to God for their words to share and their boldness to proclaim.
Finally, e be strong in the Lord
and in f the strength of his might.
g Put on h the whole armor of God,
that you may be able to stand against i the schemes of the devil.
For j we do not wrestle against flesh and blood,
but against k the rulers,
against the authorities,
against l the cosmic powers over m this present darkness,
against n the spiritual forces of evil o in the heavenly places.
Therefore p take up the whole armor of God,
that you may be able to withstand in q the evil day,
and having done all,
to stand firm.
r having fastened on the belt of truth,
and s having put on the breastplate of righteousness,
and, t as shoes for your feet,
having put on the readiness given by the gospel of peace.
In all circumstances take up u the shield of faith,
with which you can extinguish all v the flaming darts of w the evil one;
and take s the helmet of salvation,
and x the sword of the Spirit,
which is the word of God,
praying y at all times z in the Spirit,
a with all prayer
To that end
b keep alert with all perseverance,
making c supplication
for all the saints,
and d also for me,
that words may be given to me
in opening my mouth e boldly
to proclaim f the mystery of the gospel,
for which I g am an ambassador h in chains,
that I may declare it boldly,
as I ought to speak.