You don't have to feel joyful in order to live joyfully (Philippians 4)

PHILIPPIANS 4:4Rejoice in the Lord always; again I will say, rejoice.

"Rejoice" means "to demonstrate joy." It is an active word. More than something you feel, rejoicing is something you do. 

Nat King Cole sang about rejoicing.

Smile though your heart is aching
Smile even though it's breaking
When there are clouds in the sky, you'll get by
If you smile through your fear and sorrow
Smile and maybe tomorrow
You'll see the sun come shining through for you
Light up your face with gladness
Hide ev'ry trace of sadness
Although a tear may be ever so near
That's the time you must keep on trying
Smile, what's the use of crying
You'll find that life is still worthwhile
If you just smile

He was mostly right. What he didn't mention (but Paul did) is that we can rejoice IN THE LORD. Circumstances change, emotions fluctuate, relationships struggle but Jesus Christ is the same yesterday, today and forever.

Sometimes we struggle to live joyfully because we are rejoicing in the wrong thing. If your greatest joy derives from your team winning a game, you'll not always be joyful because they won't always win. If your greatest joy is gleaned from your job, you won't always be joyful because your job will sometimes be miserable. If your greatest joy is in your children, or spouse, or significant other, or a pursuit of a significant other; you'll not always be joyful because people will let you down.

Paul says to ALWAYS live joyfully because of Jesus! In every situation, remind yourself that He is present, He is powerful, and He is passionate for your growth. Then, regardless of what is happening and regardless of how you feel...

REJOICE!