When joy is shared joy multiplies many times. If one is on a island and got a million dollars in lottery, but no body to share the joy with is not very happy. The same person in the midst of family and friends to share the joy will be immensely happy. There is joy in sharing. Sharing is union. Union is happiness. When two friends that have not met for 40 years suddenly meet in airport, they forget the surroundings in their union. They become one and experience immense joy. Mothers experience the same joy with children. Conjugal joy at the peak experience is the same joy of union.
In union, boundaries dissolve and merger takes place. Two becomes one. This oneness and union produces joy. The name for this union is Love, expansion love or Divine love. The more the union, more the experience of this joy and happiness. When all of duality merges into oneness the joy is infinite. This infinite, unending joy is called Ananda (bliss). All celebrations and festivals foster this sharing, giving and togetherness. Thus they help us experience this joy of union, oneness, little by little. These small glimpses of joy through union should expand ultimately to union of all diversity into our source of absolute Oneness and UNITY. That is Nirvana, Self-realization, Moksha or Liberation.