Nehemiah said, “Go and enjoy choice food and sweet drinks, and send some to those who have nothing prepared. This day is sacred to our Lord. Do not grieve, for the joy of the Lord is your strength.”
This is even from the old testament - you know that bit of the bible that we tend to think of as the 'harsher' God.
God is the same yesterday, today and forever.
The joy of the Lord is your strength. Not - God will give you joy if you a strong and stick it out.
His joy is your strength. Rejoice in Him.