Finally. Resuming his general exhortations, he again enjoins them to be strong, -- to summon up courage and vigor; for there is always much to enfeeble us, and we are ill fitted to resist. But when our weakness is considered, an exhortation like this would have no effect, unless the Lord were present, and stretched out his hand to render assistance, or rather, unless he supplied us with all the power. Paul therefore adds, in the Lord. As if he had said, "You have no right to reply, that you have not the ability; for all that I require of you is, be strong in the Lord." To explain his meaning more fully, he adds, in the power of his might, which tends greatly to increase our confidence, particularly as it shews the remarkable assistance which God usually bestows upon believers. If the Lord aids us by his mighty power, we have no reason to shrink from the combat. But it will be asked, What purpose did it serve to enjoin the Ephesians to be strong in the Lord's mighty power, which they could not of themselves accomplish? I answer, there are two clauses here which must be considered. He exhorts them to be courageous, but at the same time reminds them to ask from God a supply of their own deficiencies, and promises that, in answer to their prayers, the power of God will be displayed.

Finally, my brethren, be strong in the Lord - Paul had now stated to the Ephesians the duties which they were to perform. He had considered the various relations of life which they sustained, and the obligations resulting from them. He was not unaware that in the discharge of their duties they would need strength from above. He knew that they had great and mighty foes, and that to meet them, they needed to be clothed in the panoply of the Christian soldier. He closes, therefore, by exhorting them to put on all the strength which they could to meet the enemies with which they had to contend; and in the commencement of his exhortation he reminds them that it was only by the strength of the Lord that they could hope for victory. To be "strong in the Lord," is:
(1) to be strong or courageous in his cause;
(2) to feel that he is our strength, and to rely on him and his promises.

Finally - Having laid before you, your great and high calling, and all the doctrines and precepts of the Gospel, it is necessary that I should show you the enemies that will oppose you, and the strength which is requisite to enable you to repel them.
Be strong in the Lord - You must have strength, and strength of a spiritual kind, and such strength too as the Lord himself can furnish; and you must have this strength through an indwelling God, the power of his might working in you.

(12) Finally, my brethren, be strong in the Lord, and in the power of his might.
(12) He concludes the other part of this epistle with a grave exhortation, that all are ready and fight constantly, trusting in spiritual weapons, until their enemies are completely put to flight. And first of all he warns us to take up the armour of God, for with it alone may our enemy be dispatched.

Finally, my brethren,.... This is the conclusion of the apostle's exhortations, in which he addresses the saints as his brethren; which appellation he uses, not merely as a familiar way of speaking among the Jews, but in regard to them as regenerate persons, and of the same family and household of God with himself; and he calls them so, to show his humility, and as a proof of his affection to them, and with a design to encourage them to their duty, as follows:
be strong in the Lord, and in the power of his might; which is directed to, partly on account of the things before exhorted to, which could not be performed in their own strength; and partly with respect to their many and potent enemies hereafter mentioned, against whom they had no might nor power of their own; and therefore the apostle points out the Lord Jesus Christ unto them, in whom are strength, power, and might, even everlasting strength, to enable them to perform their duty, and to fight against every enemy, sin, Satan, and the world; for though they are weak, and strength in themselves, and can do nothing of themselves, and without Christ; yet since there is strength in him, which is communicable to them, they may expect it from him, and depend upon it; and they may come at, or strengthen themselves in it, and by it, by meditation on it, by prayer for it, by waiting on Christ in his own ways, by exercising faith upon him, and through the Spirit, who strengthens them from him with might in the inward man.

Spiritual strength and courage are needed for our spiritual warfare and suffering. Those who would prove themselves to have true grace, must aim at all grace; and put on the whole armour of God, which he prepares and bestows. The Christian armour is made to be worn; and there is no putting off our armour till we have done our warfare, and finished our course. The combat is not against human enemies, nor against our own corrupt nature only; we have to do with an enemy who has a thousand ways of beguiling unstable souls. The devils assault us in the things that belong to our souls, and labour to deface the heavenly image in our hearts. We must resolve by God's grace, not to yield to Satan. Resist him, and he will flee. If we give way, he will get ground. If we distrust either our cause, or our Leader, or our armour, we give him advantage. The different parts of the armour of heavy-armed soldiers, who had to sustain the fiercest assaults of the enemy, are here described. There is none for the back; nothing to defend those who turn back in the Christian warfare. Truth, or sincerity, is the girdle. This girds on all the other pieces of our armour, and is first mentioned. There can be no religion without sincerity. The righteousness of Christ, imputed to us, is a breastplate against the arrows of Divine wrath. The righteousness of Christ implanted in us, fortifies the heart against the attacks of Satan. Resolution must be as greaves, or armour to our legs; and to stand their ground or to march forward in rugged paths, the feet must be shod with the preparation of the gospel of peace. Motives to obedience, amidst trials, must be drawn from a clear knowledge of the gospel. Faith is all in all in an hour of temptation. Faith, as relying on unseen objects, receiving Christ and the benefits of redemption, and so deriving grace from him, is like a shield, a defence every way. The devil is the wicked one. Violent temptations, by which the soul is set on fire of hell, are darts Satan shoots at us. Also, hard thoughts of God, and as to ourselves. Faith applying the word of God and the grace of Christ, quenches the darts of temptation. Salvation must be our helmet. A good hope of salvation, a Scriptural expectation of victory, will purify the soul, and keep it from being defiled by Satan. To the Christian armed for defense in battle, the apostle recommends only one weapon of attack; but it is enough, the sword of the Spirit, which is the word of God. It subdues and mortifies evil desires and blasphemous thoughts as they rise within; and answers unbelief and error as they assault from without. A single text, well understood, and rightly applied, at once destroys a temptation or an objection, and subdues the most formidable adversary. Prayer must fasten all the other parts of our Christian armour. There are other duties of religion, and of our stations in the world, but we must keep up times of prayer. Though set and solemn prayer may not be seasonable when other duties are to be done, yet short pious prayers darted out, always are so. We must use holy thoughts in our ordinary course. A vain heart will be vain in prayer. We must pray with all kinds of prayer, public, private, and secret; social and solitary; solemn and sudden: with all the parts of prayer; confession of sin, petition for mercy, and thanksgiving for favours received. And we must do it by the grace of God the Holy Spirit, in dependence on, and according to, his teaching. We must preserve in particular requests, notwithstanding discouragements. We must pray, not for ourselves only, but for all saints. Our enemies are mighty, and we are without strength, but our Redeemer is almighty, and in the power of his mighty we may overcome. Wherefore we must stir up ourselves. Have not we, when God has called, often neglected to answer? Let us think upon these things, and continue our prayers with patience.

my brethren--Some of the oldest manuscripts omit these words. Some with Vulgate retain them. The phrase occurs nowhere else in the Epistle (see, however, Ephesians 6:23); if genuine, it is appropriate here in the close of the Epistle, where he is urging his fellow soldiers to the good fight in the Christian armor. Most of the oldest manuscripts for "finally," read, "henceforward," or "from henceforth" (Galatians 6:17).
be strong--Greek, "be strengthened."
in the power of his might--Christ's might: as in Ephesians 1:19, it is the Father's might.

Be strong in the Lord. He comes to his final admonition. They are engaged in a fearful warfare (Ephesians 6:12). They need to be equipped for it. Let them be strong by using the armor, weapons and means which are named in the next section.

Brethren - This is the only place in this epistle where he uses this compellation. Soldiers frequently use it to each other in the field. Be strong - Nothing less will suffice for such a fight: to be weak, and remain so, is the way to perish. In the power of his might - A very uncommon expression, plainly denoting what great assistance we need as if his might would not do, it must be the powerful exertion of his might.