Ephesians 6:10 >>
Finally, my brethren, be strong in the Lord, and in the power of his might.
"Finally, my brethren"
Paul is wrapping up his letter with the final instructions to his brothers and sisters in Christ. What is to come in the next verses is the summarization of all that Paul taught throughout the epistle. The Ephesian brethren will be exhorted to apply this letter to their lives.
"be strong in the Lord"
Christians are "in Christ". They got there by being baptized into Him, (Galatians 3:27, Romans 6:3). Paul is encouraging his brethren to be strong, much like what he said to the Corinthian Christians near the end of their first letter.
"Therefore, my beloved brethren, be ye stedfast, unmoveable, always abounding in the work of the Lord, forasmuch as ye know that your labour is not in vain in the Lord."
Be steadfast, strong and unmoveable, in Christ.
"and in the power of his might."
Paul leaves no doubt to the Ephesians as to Christ's power, mentioning it twice in Ephesians 1:19, "And what is the exceeding greatness of his power to usward who believe, according to the working of his mighty power," and again in Ephesians 3:16, "That he would grant you, according to the riches of his glory, to be strengthened with might by his Spirit in the inner man;"
By telling the Ephesians to "be strong in the Lord and in the power of His might, it is evident that there is a choice here. To either "be strong" or "not to be strong" in both the Lord and His power. One can by one's own free will or actions choose either of these possibilities. If it were not possible to choose, Paul would not have encouraged them to "be strong". There would have been no need.