Simchat Chatan V'kalla
There is a tremendous mitzva to somehow contribute and participate in making a bride and groom happy on their wedding day, especially if one is attending the wedding. This mitzva, known as simchat chatan v'kalla, is actually considered the highest form of chesed which one can show for another person. The mitzva of simchat chatan v'kalla is actually in effect for the entire week of sheva berachot celebrations. The merits of this mitzva are so great that even the greatest sinners can earn themselves significant reprieve by fulfilling this mitzva alone.
No one should think for a moment that it is beneath their dignity to entertain a bride and groom, even if it includes otherwise silly activities. Even the greatest of all sages were meticulous in fulfilling this mitzva. We are taught the God Himself tended to Adam and Eve on their wedding day including having braided Eve's hair in preparation for the ceremony and it was the angels who provided the musical accompaniment.
The more charitable element to the mitzva of simchat chatan v'kalla is known as "hachnassat kalla", which means "providing for a bride". This term generally refers to ensuring that the immediate financial needs of a bride are tended to, particularly with regards to disadvantaged brides. Personal acts of kindness which are shown to a bride are also included in this mitzva. As one can imagine, weddings are a tremendous and sometimes unbearable expense. Contributing funds to help offset the costs of a wedding is considered to be one of the highest forms of charity. Even lending the couple money to help cover their wedding expenses is a mitzva.
It is especially meritorious to attend a wedding which is expected to have minimal attendance, in order to help make the new couple feel important. It is best that the men remain primarily with the groom and not venture into the bridal area for too long so as not to unnecessarily mix with the women. The obligation to gladden a bride applies to the groom himself, as well. In fact, a groom accomplishes this mitzva by merely attending his own wedding meal. Actually, a groom has an obligation to gladden his wife for seven days following their wedding, and to a lesser extent, the entire first year of marriage. Attending a wedding takes precedence over attending one's regularly scheduled Torah study sessions.
The mitzva of hachnassat kalla is not an autonomous one but is also a concurrent fulfillment of the mitzva of v'ahahavta l'reacha kamocha, to love a fellow Jew as oneself, a Biblical mitzva in its own right. Even just a few complimentary words to the bride and groom is deemed as having contributed to their happiness.It is even permitted to lie and offer false compliments to the bride and groom if doing so would bring them greater happiness. It is forbidden to attend a wedding without doing something to contribute to the happiness of the bride and groom.One should also dance before the bride and groom and give them wedding gifts. A component of the mitzva of simchat chatan v'kalla requires that there be live music played at a wedding.
One who is careful to fulfill the mitzva of simchat chatan v'kalla is considered to have brought an offering in the Beit Hamikdash and rebuilt the ruins of Jerusalem. It is also said that those who fulfill this mitzva will be showered with extraordinary blessings when the final redemption takes place. There is even a legend that the father of Rabbi Ovadia Yosef, Rabbi Yaakov, merited to have a son like Rabbi Ovadia in the merit of having been meticulous in this mitzva.
There is an interesting custom in Chassidic circles, known as the "mitzva tantz", to invite distinguished guests to dance with the bride at her wedding. This dance usually takes place towards the end of the evening. The "dance" in this context is unlike what one might think, but rather, the bride holds one end of a long rope or gartel while her dancing "partner" holds the other end. It is usually just the partner who dances to the music, while the bride remains stationary. The mitzva tantz, complete with its distinguished participants, is also said to be a way of bestowing honor upon the bride and groom.
We are told that one of the first questions one is asked upon arrival in Heaven is whether or not one was involved in fulfilling such mitzvot during one's lifetime.Indeed, the principal rewards for the mitzva of hachnassat kalla are reserved for the Next World. There is hardly a community without a hachnassat kalla foundation where people can contribute on an ongoing basis to ensure that there are always funds readily available for needy brides.
 Berachot 6b, Tur E.H. 65
 Pirkei D'rabbi Eliezer 16
 Pirkei D'rabbi Eliezer 16; Yalkut Shimoni;Shoftim 70
 Pirkei D'rabbi Eliezer 17, Yalkut Shimoni;Melachim 247,232
 Chavot Yair 205
 Ketubot 17a;Rashi
 Pirkei D'rabbi Eliezer 16
 Nidda 45b
 Pirkei D'rabbi Eliezer 16
 Y.D. 249:15, Chochmat Adam 145:2
 Taz E.H. 65:2, Aruch Hashulchan E.H. 65:4
 Pesachim 49a
 Rambam Ishut 10:12, Ramban;Bereishit 29:27, Chelkat Mechokek E.H. 64:4
 Ketubot 17a, Rema E.H. 65:1
 Rambam Avel 14:1
 Rashi;Berachot 6b
 Ketubot 17a
 Perisha 65:2
 Aruch Hashulchan E.H. 65:3
 Ta'amei Haminhagim 980, Teshuvot V'hanhagot 3:404
 Likutei Maharich, Minhag Yisrael Torah p.207
 Be'er Moshe 4:131
 Hanesuin K'hilchatam Chapter 13, note 89
 Shabbat 31a;Maharsha
 Peah 1:1