In a letter to the first century church, St. Paul told them to “Be joyful always.” The fact that it’s written in the form of a command is very significant. What we have here is not a suggestion, an encouragement or a piece of wise advice. It’s not implying that the greatest griefs of life can by easily replaced by some superficial happiness. This is the Word of God ordering us to be joyful! So, you say, “How do I do that? I can’t control how I feel.” And that’s the point exactly.
This quote is talking about actions, not feelings. Feelings can’t be commanded. Feelings are emotional responses to both what’s inside of us and to what’s happening to us on the outside. Feelings are extraordinarily difficult to control. Not even God commands us how or what to feel. But he does command us what to do. And one of those commands is to “be joyful.” Let’s compare it to going to the doctor because you feel run down and tired all the time. Your physician would not tell you to “stop feeling tired” or order you to “feel energetic.” But she might say, “Exercise 30 minutes every day.”
She knows that if you take her advice and go home and exercise, the action of exercising will have the byproduct of altering your feeling of tiredness.
Joy is an action, not an emotion. And the action of joy has the power to change our emotions.