Literally, "Strengthen yourself in the Lord"
Natural effort and ideas will not work against these spiritual forces.
Though this command is "imperative" giving us the responsibility. We are to take God's power and use it. In other places in the NT God does the empowering:
God's power has already been mentioned in Ephesians by Paul:
It is the power to resist the forces in the world who are hostile to God and his ways and his plans.
It is a strength that God has been using against the forces of evil since the beginning.
Three words are used in this verse to refer to power:
This list of "power" words is Paul trying to emphasize the extreme power of God like he did when he tried to capture it in his words in Eph. 3:16-17
Also, see Colossians 1:11 and Isaiah 40: 20-26
Luke 11:21-22 a strong man is stripped of his "panoply" by a stronger man
"Panoply" means literally "whole or complete armor"
The church is now fighting God's battle.
In Eph. 4:22-24 we are to put off the old man and put on the new.
This new creation is to engage in the battle that is still raging.
Christ won the victory but the battle needs to be fought, just like when Christ returns the war on earth will continue for a period. (Zech. 14:14; Dan. 12:11)
This is a real battle as alluded to in 1 Corinthians 15:24-25.
2 Corinthians 10:3-5 - the weapons are siege engines that demolish arguments and lofty philosophies that come against God's knowledge.
Colossians 2:8 warns against being taken captive through hollow and deceptive philosophies.
Ephesians 4:14 mentions the teaching and cunning craftiness of men
Ephesians 6:11 it is the wiles of the devil that have to be resisted.
Some of the wiles of the devil are:
Principalities, Powers, etc. have already been mentioned as neutral in:
A portion (1/3, Rev. 12:4)) rebelled and are now hostile to God having been disarmed in Colossians 2:15 on the cross.
Disarmed posers are no threat to the saved people who are covered with the panoply of God.