Genesis 3 v. 10 . The book of Philippians majors on this question. The word for joy comes 13 times in its 4 chapters but it seems to be a very different joy from that induced by the entertainers. This is a strange joy because it is commanded. No, the secret here is who we are to rejoice in, it is in our relationship with our Lord.
Christian joy is somewhat similar to the joy experienced by a couple deeply in love.
Literally, it may begin with explosive enthusiasm but over the years it will mature if nurtured into a close permanent friendship. The next few verses explain this clearly. Having commanded his readers to Rejoice in the Lord , Paul suddenly changes his tone. Verse 2 reads, Watch out for those dogs, those men who do evil, those mutilators of the flesh. This is an even stronger warning in the original Greek as the word for watch out is repeated three times.