Nehemiah 8:10 NIV
Nehemiah said, “Go and enjoy choice food and sweet drinks, and send some to those who have nothing prepared. This day is holy to our Lord. Do not grieve, for the joy of the Lord is your strength.”

The joy of the Lord is your strength. 

I look at it this way: In a race, battle, journey or any activity, if you take away the strength of a person, he or she will start to lose. That person won’t be able to do anything anymore. They’ll simply become weak and useless.

Ultimately, they’ll fail.

Satan understands this very well. In our case he knows what our strength is.

The joy of the Lord.

He knows that in order to defeat you, all he has to do is to take away your strength—that is, your joy.

So, He attacks your joy relentlessly in order to keep you weak and defeated.

He attacks your joy by pointing you to your challenging circumstances: your bills; your rent; your debts; your lack.

He attacks your joy by reminding you of your past mistakes: Your sins; your flaws; the shameful things you’ve done in the past.

He attacks your joy by poisoning your mind with the negative things other people have said about you; how they’ve rejected you; how they’ve treated you.

And if he has his way, you plunge into sadness, discouragement and defeat.

This is why I protect my joy. This is why I choose joy. And this is why the Holy Spirit tells us to rejoice in Him always!

Philippians 4:4 NIV
Rejoice in the Lord always. I will say it again: Rejoice!

Declare this right now:

I chose joy. I will never let Satan or anyone steal my joy. I will rejoice in the Lord always.