This expression "Be strong" does not mean "Be strong in body," but "Be strong in mind;" "Be strong in spirit;" "Be brave."
An order like this could not have been a mere mockery, an order which Joshua was unable to obey. The word which bade him be strong was an assurance at the same time that if he would, he might be strong according to his day.
I. The first secret of true courage is to know and be sure that we have some power. Hence the wisdom of the maxim of the ancients, "Know thyself" learn to see what thy real capacity is, and knowing that, shrink not from venturing on putting it to the proof. It is not too much to say that all men go wrong by underestimating themselves? For what deeper self-depreciation is there than for a man to live in the world forgetful of what he is brought here for forgetful of his Christian privileges, of his Christian name, of his Christian freedom?
II. We all have some power; the question is, How much and what? That is the question we should ask ourselves every day; it is the great question of our early life especially, for on the right answering of it all our success depends. Our weaknesses guarded against often become our strength; and our best lessons, if we heed them, are our mistakes. Joshua's strength was a knowledge of his weakness. Beware of thinking you have no strength because you are not omnipotent. God says to us all, whatever worthy work we are entering upon, "Be of good courage; be strong!"
A. Jessopp, Norwich School Sermons,p. 97.
References: Joshua 1:9. J. Ellison, Christian World Pulpit,vol. xv., p. 305; Congregationalist,vol. vii., p. 400. Joshua 1:16-18. Parker, Pulpit Analyst,vol. i., p. 626. 1, etc. G. Gilfillan, Alpha and Omega,vol. i., p. 156. 2 A. Saphir, Found by the Good Shepherd,p. 383.