"My flesh and my heart may fail, but God is the strength of my heart and my portion forever." Psalm 73:26
This verse explains the power we have when we rely on God for strength. When it says "my flesh and heart" that refers to a whole man, his body and his soul. So when the whole body fails, our human strength has run out, whether that be through sickness, health, sorrow or any other weakness. On our own, we are helpless once our flesh and heart have failed.
But it doesn't end there. When we are exhausted and our bodies are failing, God gives us a strength that gives us life, joy, and endless peace in even the hardest of situations. In circumstances when fear and doubt should be overpowering us, God's love surrounds us and keeps us alive. But not only that, this power that God gives us will satisfy us to the core everyday. No source of happiness from any earthly friend, or from fame or wealth will give us the joy and strength that is in Jesus.
This verse has a poetic feel to it by the way in which it was written. The second part of the sentence is inverted and the word "heart" is mentioned first, instead of second. This is because of the importance of how God takes the weaknesses we have and transforms us from the inside out. Starting with the heart. Once He has given us the strength in our heart, on the inside, His joy will last with us forever.
Tomorrow's Bible In a Year Passage: Psalm 74-76; Romans 9:16-33