When you get a certain age or have a family history of heart problems, like high blood pressure that can cause a heart attack, we go to the doctor to get medicine to keep the blood pressure where it is supposed to be, so it makes the heart function right. In Proverbs 17:22, it says A Joyful heart is good medicine! It is better than any medicine on the market.
Paul tells the Colossians that his desire is to encourage their hearts through his labors for the Lord. He wants them, and us, to have a cheerful heart, which keeps us from falling victim to the world around us.