The purpose of the rabbi at a wedding is to ensure that the extremely detailed wedding halachot, as set out by the Shulchan Aruch, are followed correctly. If not, the wedding might not be kosher.
A Jewish marriage includes: a written document (ketuba); a financial transaction (ring) in front of two kosher witnesses; and physical intimacy.
The witnesses must be shomer Shabbat Jewish men.
The bride and groom should confirm verbally that these are the two (and the only two) witnesses that they want.
The groom must confirm that he acquired and owns the ring.
The groom must say Harei at mekudeshet li … to the bride and place the ring on her (index) finger.
The ketuba must be kosher.
Before the chuppa, someone (anyone, including women) must fill in (no safrut is required for this): the Hebrew names of the bride and groom; the date the wedding is taking place; the wedding location (city, etc.); and that a kinyan was made.
The ketuba must be signed by two kosher witnesses.
Giving Information about Potential Mate
You must tell whatever you know that is relevant about a potential date that someone is considering marrying.
NOTE: Since it is for a purpose, there is no issue of lashon ha’ra.
Dating only People You May Marry
You should date only people whom you may marry.
A convert must have had a kosher conversion.
A cohen may not date divorcees, converts, or a woman both of whose parents converted before she was born.
The person must not be a mamzeir or child of mamzeirim (offspring of a forbidden union).
NOTE: A mamzeir is permitted to marry another mamzeir.
Checking Jewish Lineage
If there may be any question about the Jewish lineage of a bride-to-be or bridegroom, his or her female antecedents should be confirmed as having been Jewish (born of a Jewess OR halachically converted) back to when a shomeret Shabbat woman has been positively identified (or back as far as possible). As a practical matter, three or four generations may be as far back as most Jews can be traced.
Also, make sure that if there was any divorce, that the divorce was kosher, with a get.
Checking on Whether the Couple May Marry
The mesader kidushin (organizer of the wedding ceremony) should research whether the couple is permitted to marry. This should be done well in advance of the wedding date.
Not Seeing Each Other
Some people have a custom for a groom and bride not to see each other for the seven days leading up to their wedding.
Bride and Groom Fast
The bride and groom must not eat or drink any food from 72 minutes before sunrise on the day of their wedding, even if their wedding takes place after sunset on the following Jewish calendar day.
Bride to the Mikva
The bride must go to the mikva before she may have relations with her husband.
Groom to the Mikva
The groom should immerse himself in a mikva on his wedding day. He may immerse in the ocean, but should not be alone while immersing.
Offspring at Parent’s Re-Marriage
A child should not attend the wedding of a parent, such as if the parent gets married after divorce, after the death of first spouse, or if never married–or halachically married–before his/her child was born.
Copyright 2015 Richard B. Aiken. Halacha L’Maaseh appears courtesy of www.practicalhalacha.com Visit their website for more information.