"But those who wait upon the Lord shall renew their strength." Isaiah 40:31
How different the religion of a living soul is from the religion of a dead professor! The religion of a dead professor begins in self, and ends in self; begins in his own wisdom, and ends in his own folly; begins in his own strength, and ends in his own weakness; begins in his own righteousness, and ends in his own damnation! There is in him never any going out of soul after God, no secret dealings with the Lord, no actings of faith upon the divine perfections.
But the child of God, though he is often faint, weary, and exhausted with many difficulties, burdens and sorrows; yet when the Lord does show himself, and renews his strength, he soars aloft, and never ceases to mount up on the wings of faith and love until he penetrates into the very sanctuary of the most High. A living soul never can be satisfied except in living union and communion with the Lord of life and glory. Everything short of that leaves it empty. All the things of time and sense leave a child of God unsatisfied. Nothing but vital union and communion with the Lord of life, to feel his presence, taste his love, enjoy his favor, see his glory--nothing but this will ever satisfy the desires of ransomed and regenerated souls. This the Lord indulges his people with.
"They shall renew their strength." They shall not be always lying groaning on the ground, not always swooning away through the wounds made by sin, not always chained down by the fetters of the world, not always hunted in their souls like a partridge upon the mountains. There shall be a renewal of their strength; and in their renewal, "they shall mount up with wings as eagles; they shall run, and not be weary; and they shall walk, and not faint."