Joy is an expression of a vision of beauty, bounty and being beloved. The Gospel is about joy.

Gospel means good news.
It is the good news that the Lord loves us and has made it possible for us to be in intimate personal relationship with Him by His indwelling HolySpirit.

When we begin to grasp the Truth, we are made free whereby we experience love, peace and joy. Our joy should be untainted by fear and unbelief. It becomes full as we grow in Grace and knowledge of Christ.

On the other hand, the gift of the Lord is so magnificent that rejection of it demands expulsion into the LakeOfFire Rev 20:15. People who reject the love of the Lord and refuse to worship Him, do not have the love of the Lord and would not only not fit in heaven, they would corrupt it.