Isaiah 40:28-31 Have you not known? Have you not heard? The everlasting God, the Lord, the Creator of the ends of the earth, neither faints nor is weary. His understanding is unsearchable. He gives power to the weak, and to those who have no might He increases strength. Even the youths shall faint and be weary, and the young men shall utterly fall, but those who wait on the Lord shall renew their strength; they shall mount up with wings like eagles, they shall run and not be weary, they shall walk and not faint. 

Galatians 2:20-21 I have been crucified with Christ; it is no longer I who live, but Christ lives in me; and the life which I now live in the flesh I live by faith in the Son of God, who loved me and gave Himself for me. I do not set aside the grace of God; for if righteousness comes through the law, then Christ died in vain.