What's the difference between a party and a holy party? In general, a party is a celebration. A holy party is also a celebration, only it's a celebrates connection to the Creator. Truthfully, everyday should be a celebration of connection with the Creator, regardless of the month. However, Adar is the training grounds for constant joy. Indeed, the "Book of Formation" teaches that the character of Adar is "laughter". We laugh and laugh. We laugh caught up in the joy of the moment. We laugh to train ourselves to laugh for through the upcoming monthly cycle, beginning with the month of Nisan.
Laughter and celebration is the great equalizer. Everyone, on every level, can enjoy a celebration. A wedding is the highest of celebrations. Opposites who were apart for so long, the couple, finally unite and finally identity blend. Male and female union on every level is the highest ideal of happiness and the source of every other kind of happiness. In language of Kabbalah the Ramchal expresses it such that happiness happens when the "kindnesses" sweeten the "severities", transforming them into "sweetness". This is a technical Kabbalistic way of saying that happiness happens when male and female unite, whether cosmically or personally.
So if opposites equalize and unify in laughter and celebration at a wedding, so can everyone else. The couple sets the stage. The ripple effects of their unifying energy wave inspires people of all sorts and levels dance together and rejoice at their wedding. If this is so within the wedding hall of a human couple, how much more so is this true of the "wedding hall" of the cosmic couple - which is the whole of creation. Every kindness, every Mitzvah, causes the cosmic couple to unite. Their happiness and celebration ripples throughout the whole cosmos with bringing good cheer to all the inhabitants, the cosmic wedding guests. This is part of why there's an expectation that we perform our good deeds with much happiness and celebration - as we are bringing union to a couple so much more alive than a human couple. Can we even imagine what happiness and celebration means on that level? Wow!
From a certain angle of thought, it really could be said that the Creator created creation for the sake of happiness, celebration and laughter. There needs to be unifying for such amazing feelings to happen. Since the Creator is a perfectly seamless Oneness, in His Being alone all is already One. There's nothing to unify. So He made a creation where duality abounds. On every level, there's male and female yearning for union. Whenever He gives blessings to His creations unions happen and happiness, celebration and laughter follow. On the highest levels, it's deep cosmic laughter. On the lower levels, it's fragments of that laughter, more individualized.