Rejoice in the LORD and be glad ... Psalm 32:11
When God created the world, it was perfect. Adam and Eve had a wonderful friendship with God and were filled with joy. God made us humans for this: for fellowship with him that fills us with joy.
Then Adam and Eve disobeyed God. This had terrible consequences. Their fellowship with God was destroyed. They had to leave paradise.
But God is love, and that is why he promised to send a Saviour back then already. Through him, fellowship with God and the joy of it can be restored.