Isaiah 40:29-31

He gives strength to those who are tired; to the ones who lack power, he gives renewed energy. Even youths get tired and weary; even strong young men clumsily stumble. But those who wait for the Lord’s help find renewed strength; they rise up as if they had eagles’ wings,they run without growing weary, they walk without getting tired.

Living out our faith is a give and receive process. We give our all led by the Holy Spirit in Christ Jesus. We receive "renewed strength" from the Lord, and it is because we choose to depend upon Him fully when we are weak. We choose to receive this dimension of His grace that relentlessly looks to Jesus for every single need. 2 Cor. 12:9 says, "And He said to me, 'My grace is sufficient for you, for My strength is made perfect in weakness.' Therefore most gladly I will rather boast in my infirmities, that the power of Christ may rest upon me."