My flesh and my heart may fail, but God is the strength of my heart and my portion forever (Psalm 73:26 NIV).
The psalmist is thinking about a real possibility here. Though he is now fine, he thinks of a day when his strength would be gone. But, to our surprise, we find that he is not alarmed about this possibility. This is because he already has made sure that he has Someone to fall back on even if his strength gives out.
This Someone is God Himself. The psalmist says that God is the strength of his heart. The body may lose its strength due to aging. The mind might lose its ability to think clearly when confronted with a lot of problems. Yet these losses will not defeat the man who has made God his strength.
What does that mean? It means that the man who has made God his strength is relying not on his mental ability or physical strength. It means that such a man is aware that there is a lurking possibility of failure some day of all the natural powers that he enjoys now. Yet when that happens he will not be found unprepared. He would find strength in God. It would be like the Sun rising in the night!
The psalmist also adds that there is one more thing that gives him confidence. That is his ability to see beyond the values of possessions on earth. He knows very well that whatever inheritance he has gained and whatever valuables he has earned will do him no good when the continuing march of time will close the curtain of his life. So he has made God his portion. He knows that when all else is gone, this portion will remain!