Even the youths shall faint and be weary, and the young men shall utterly fall: But they that wait upon the LORD shall renew their strength; they shall mount up with wings as eagles; they shall run, and not be weary; and they shall walk, and not faint.

Isaiah 40:30-31

Explanation:
“Youths” and “young men” are not known for chronic fainting and falling from a lack of strength, and yet they are not immune from it. Most often those that fall in a way that brings them severe harm are the elderly. Yet Isaiah says here “even the youths…”. The point being made is that even the most physically strong among us are prone to weariness, injury, and the need for more strength. There are none that are immune from physical limitations. Then there is an incredible reality that is proposed. “They that wait upon the Lord shall renew their strength”. God is the source of strength that every single one of us need. When we go to Him and submit to Him, He will sustain us. He will renew us. What a beautiful description of the renewed person:

“…they shall mount up with wings as eagles; they shall run, and not be weary; and they shall walk, and not faint.”

One commentator put described the truth of this verse by saying:

“Far from being crushed to earth by their own helplessness, those who depend on God can stretch their wings in the effortless way of eagles and sail off on the wind.” 

Waltke

Application:

Those who go to God for strength and depend on God for what they need are going to a source of infinite supply. He is alive, and not dead. He is the Creator and is not created. He is the Sustainer. He does not run out of energy, knowledge or resource. He is completely trustworthy and will do what He has promised to do. We must find our strength in Him. To seek it somewhere else is to go to a finite, undependable source.

Response:
What is something you can do today to depend on God for strength?