Isaiah was a prophet who's oracles are laid out in the Old Testament. He based his messages on the deep bond between God and his people. In chapter 40 he gives words of encouragement and comfort to God's people.
Isaiah 40:31
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 40:28
The Lord is the everlasting God, the Creator of the ends of the earth. He will not grow tired or weary, and his understanding no one can fathom. He gives strength to the weary and increases the power of the weak.