So we may be bold in the march, and draw upon our stock of strength to the utmost. There is no fear that it will fail us. We may put all our force into our work, we shall not weaken the power which 'by reason of use is exercised,' not exhausted. For the grace which Christ gives us to serve Him, being divine, is subject to no weariness, and neither faints nor fails. The bush that burned unconsumed is a type of that Infinite Being who works unexhausted, and lives undying, after all expenditure is rich, after all pouring forth is full. And of His strength we partake.
Whensoever a man puts forth an effort of any kind whatever--when I speak, when I lift my hand, when I run, when I think-there is waste of muscular tissue. Some of my strength goes in the act, and thus every effort means expenditure and diminution of force. Hence weariness that needs sleep, waste that needs food, languor that needs rest. We belong to an order of being in which work is death, in regard to our physical nature; but our spirits may lay hold of God, and enter into an order of things in which work is not death, nor effort exhaustion, nor is there loss of power in the expenditure of power.
That sounds strange, and yet it is not strange. Think of that electric light which is made by directing a strong stream upon two small pieces of carbon. As the electricity strikes upon these and turns their blackness into a fiery blaze, it eats away their substance while it changes them into light. But there is an arrangement in the lamp by which a fresh surface is continually being brought into the path of the beam, and so the light continues without wavering and blazes on. The carbon is our human nature, black and dull in itself; the electric beam is the swift energy of God, which makes us 'light in the Lord.' For the one, decay is the end of effort; for the other, there is none. 'Though our outward man perish, yet the inward man is renewed day by day.' Though we belong to the perishing order of nature by our bodily frame, we belong to the undecaying realm of grace by the spirit that lays hold upon God. And if our work weary us, as it must do so long as we continue here, yet in the deepest sanctuary of our being, our strength is greatened by exercise. 'Thy shoes shall be iron and brass.' 'Thy raiment waxed not old upon thee, neither did thy foot swell, these forty years.' 'Stand, therefore, having your feet shod with the preparedness of the Gospel of peace.'
But this is not all. There is an advance even upon these great promises in the closing words. That second clause of our text says more than the first one. 'Thy shoes shall be iron and brass,' that promises us powers and provision adapted to, and unexhausted by, the weary pilgrimage and rough road of life. But 'as thy days, so shall thy strength be,' says even more than that. The meaning of the word rendered 'strength' in our version is very doubtful, and most modern translators are inclined to render it 'rest.' But if we adhere to the translation of our version, we get a forcible and relevant promise, which fits on well to the previous clause, understood as it has been in my previous remarks. The usual understanding of the words is 'strength proportioned to thy day,' an idea which we have found already suggested by the previous clause. But that explanation rests on, or at any rate derives support from, the common misquotation of the words. They are not, as we generally hear them quoted, 'As thy day, so shall thy strength be,'--but 'day' is in the plural, and that makes a great difference. 'As thy days, so shall thy strength be,' that is to say: the two sums--of 'thy days' and of 'thy strength'--keep growing side by side, the one as fast as the other and no faster. The days increase. Well, what then? The strength increases too. As I said, we are allied to two worlds. According to the law of one of them, the outer world of physical life, we soon reach the summit of human strength. For a little while it is true, even in the life of nature, that our power grows with our days. But we soon reach the watershed, and then the opposite comes to be true. Down, steadily down, we go. With diminishing power, with diminishing vitality, with a dimmer eye, with an obtuser ear, with a slower-beating heart, with a feebler frame, we march on and on to our grave. 'As thy days, so shall thy weakness be,' is the law for all of us mature men and women in regard to our outward life.