'Be strong.' Then strength is a duty; then weakness is a sin. Then the amount of strength that we possess and wield is regulated by ourselves. We have our hands on the sluice. We may open it to let the whole full tide run in, or we may close it till a mere dribble reaches us. For the strength which is strength, and not merely weakness in a fever, is a strength derived, and ours because derived. The Apostle gives the complete version of the exhortation when he says: 'Finally, my brethren,' that Omega of command which is the Alpha of performance, 'be strong in the Lord and in the power of His might.' Let Christ's strength in. Open the heart wide that it may come. Keep yourself in continual touch with God, the fountain of all power. Trust is strength, because trust touches the Rock of Ages.
For this reason the commandment to be strong and of good courage is in the text based upon this: 'As I was with Moses, so I will be with thee. I will not fail thee nor forsake thee.' Our strength depends on ourselves, because our strength is the fruit of our faith. And if we live with Him, grasping His hand and, in the realising consciousness of our own weakness, looking beyond ourselves, then power will come to us above our desire and equal to our need. The old victories of faith will be reproduced in us when we say with the ancient king, 'Lord! We know not what to do, but our eyes are up unto Thee.' Then He will come to us, to make us 'strong in the Lord and in the power of His might.' 'Wait on the Lord and He will strengthen thine heart; wait, I say, on the Lord.'
But courage is duty, too, as well as strength. Power and the consciousness of power do not always go together. In regard to the strength of nature, courage and might are quite separable. There may be a strong coward and a weak hero. But in the spiritual region, strength and courage do go together. The consciousness of the divine power with us, and that alone, will make us bold with a boldness that has no taint of levity and presumption mingled with it, and never will overestimate its own strength. The charge to Joshua, then, not only insists upon the duty of strength, but on the duty of conscious strength, and on the duty of measuring the strength that is at my back with the weakness that is against me, and of being bold because I know that more and 'greater is He that is with me than are they that be with them.'
II. So much, then, for the first of the exhortations here. Now look next at the duty of implicit obedience to the word of command.
That is another soldierly virtue, the exercise of which sheds a nobility over the repulsive horrors of the battlefield. Joshua had to be fitted to command by learning to obey, and, like that other soldier whose rough trade had led him to some inkling of Christ's authority by its familiarising him with the idea of the strange power of the word of command, had to realise that he himself was 'under authority' before he could issue his orders.
Courage and strength come first, and on them follows the command to do all according to the law, to keep it without deflection to right or left, and to meditate on it day and night. These two virtues make the perfect soldier-courage and obedience. Daring and discipline must go together, and to know how to follow orders is as essential as to know how to despise dangers.
But the connection between these two, as set forth in this charge, is not merely that they must co-exist, but that courage and strength are needed for, and are to find their noblest field of exercise in, absolute acceptance of, and unhesitating, swift, complete, unmurmuring obedience to, everything that is discerned to be God's will and our duty.