They seem to be words that have the same meaning don’t they? But there is a fundamental difference between the two. Joy can be felt and known even when you feel sad and depressed, happiness can only be felt when you feel happy. Your circumstances have an effect on happiness, but joy is not subject to feelings or circumstances. Joy is felt and known by those who know Who their salvation depends on and salvation can only be known and felt through Jesus Christ.
Christians have joy in their hearts because of the grace that we’ve been given through accepting Jesus as our Savior. We have the joy of being loved by our Creator because He wants to love us and not because of anything that we deserve. Because we don’t deserve His love, it is a gift by grace through faith in Him. The joy of salvation is something that the world around us cannot understand nor can it comprehend it at all. Salvation doesn’t make sense to the world around us but fellow believers know it and can feel the joy of being known and loved.
Happiness is dependent on our situation and our feelings and has very little to do with the source of our salvation. We derive happiness from food and our family and from paying off bills. Happiness is a very human feeling that is totally dependent on your situation and very little else. It can be taken away at any time so it is very fragile, while joy is eternal when your joy comes from your relationship with Jesus your Savior. No one can take your joy from you because it is only truly found in Jesus Christ. Once you have a relationship with Him, your joy in that relationship will be yours forever. The “joy of the Lord is your strength“!