I. We have, first, the prophet's appeal to the familiar thought of an unchangeable God as the antidote to all despondency and the foundation of all hope. The life of men and of creatures is like a river, with its source and its course and its end. The life of God is like the ocean, with joyous movement of tides and currents of life and energy and purpose, but ever the same and ever returning upon itself. Jehovah, the unchanged, unchangeable, inexhaustible Being, spends and is unspent; gives and is none the poorer; works and is never wearied; lives and with no tendency to death in His life; flames with no tendency to extinction in the blaze.
II. Notice, next, the unwearied God giving strength to wearied men. The more sad and pathetic the condition of feeble humanity by contrast with the strength, the immortal strength, of God, the more wondrous is that grace and power of His which are not contented with hanging there in the heavens above us, but bend right down to bless us and to turn us into their own likeness. It is much to preserve the stars from wrong; it is more to restore and to bring power to feeble men. It is much to uphold all those that are falling so that they may not fall; but it is more to raise up all those that have fallen and are bowed down.
III. The last thing in these words is, the wearied man lifted to the level of the unwearied God and to His likeness. "They that wait upon the Lord shall renew their strength." That phrase means, of course, the continuous bestowment in unintermitting sequence of fresh gifts of power; as each former gift is exhausted, more is required. Grace abhors a vacuum, as nature does; and just as the endless procession of the waves rises on the beach, or as the restless network of the moonlight irradiation of the billows stretches all across the darkness of the sea, so that unbroken continuity of strength after strength gives grace for grace according to our need, and as each former supply is expended and used up God pours Himself into our hearts anew. That continuous communication leads to the perpetual youth of the Christian soul.
A. Maclaren, A Year's Ministry,2nd series, p. 293.
References: Isaiah 40:28-31. H. F. Burder, Sermons,p. 263.Isaiah 40:29. Preacher's Lantern,vol. i., p. 444.Isaiah 40:30; Isaiah 40:31. J. B. Heard, Christian World Pulpit,vol. xxiv., p. 308.