At a house that I used to own, I had the most gorgeous lilac bushes in the backyard. Every spring they were adorned by huge purple blossoms. I left the windows open so I could smell their sweet fragrance. As soon as it got a little warmer, the blossoms died off, and that aroma was gone. So every spring I hoped I wouldn't be traveling when the lilacs bloomed.
Human beings are like those blossoms. In Isaiah 40:6-7, we read, "All flesh is grass, and all its loveliness is like the flower of the field. The grass withers, the flower fades, because the breath of the Lord blows upon it; surely the people are grass."
Your body was designed by God for temporary use only. It was not designed for eternal purposes ... even though people act like it was. They look for the "Fountain of Youth," and try to figure out ways to continue to appear youthful. There's nothing wrong with that, but there comes a point where it just doesn't work! You can pull it off for a while, but eventually your body catches up with you, and people know: You're getting old!
God designed the body for temporary residency. Paul called it a "tent" in 2 Corinthians 5. Would you like to live in a tent for years? It may be fun for a few days, but the fun quickly wears off and you want something permanent.
That's why God in His graciousness designed your body to fizzle out. You won't have to live with that body forever. God will give you a new model ... one that's not susceptible to the diseases of this life ... one that will never decay. No wonder that Paul said, "In this we groan, earnestly desiring to be clothed with the heavenly dwelling place ... for to be absent from the body is to be present with the Lord" (2 Corinthians 5:2, 8).
Our bodies are fading and withering. They're passing away, just as this world is passing away. So should we just ignore them? No, far from it. (I try to keep mine as fit as I can!) What I mean is that we should concentrate on what is everlasting -- God, His kingdom, and His Word. "The grass withers, the flower fades, but the word of our God stands forever" (Isaiah 40:8).
So as you lace up your running shoes or jump on your bicycle (or when you smell the lilacs!), always remember that the things of this world are fleeting. God, in His mercy and His love, has a "heavenly dwelling place" in store for you.