After the Ketuba is read, it is signed by two witnesses. The role of the witnesses is obviously witnessing to the marital status of the couple when necessary. In this respect, the requirement of the presence of witnesses in a Jewish wedding is similar to the requirement of witnesses in any other legal, religious or secular events and ceremonies. Most states in the United States, for example, require the presence of two witnesses in a civil marriage (though in some states, like California, you can have a private wedding without witnesses).
In Jewish law, witnesses play another very important role. The witnesses actually validate the marriage. Technically speaking, the presence of a rabbi is not a requirement sine-qua-non for the validity of a Jewish marriage, as it is for other religions, or as it is the presence of a judge in a civil marriage. In theory, all that is needed for a Jewish couple to be considered legally married is the presence of two witnesses during the key moments of the ceremony (see below). The witnesses act as “notaries” who validate and give a public (as opposed to private) status to the marriage ceremony. Without the presence of two witnesses, a ceremony of Jewish marriage is invalid, even if a rabbi was present.
The presence of witnesses is required twice during the ceremony:
(1) qiddushin: When the groom gives the bride the ring, saying: “Behold you are consecrated to me as my wife, by this ring, according to the law of Moses and Israel.”
(2) Ketuba: When the Ketuba is accepted by the bridegroom through the qinyan. The two witnesses also sign the Ketuba.
Although halakhically not necessary, in many communities it is customary for those who act as witnesses of the act of qiddushin to be also the witnesses of the qinyan and sign the Ketuba.
According to what we have explained earlier, that the witnesses actually validate the marriage ceremony, the reader will understand that one of the most important responsibilities of the rabbi who presides the wedding ceremony, perhaps the most critical responsibility, is to select the witnesses. Because if a witness is not suitable to act as such, the marriage is not valid.
We will see now some rules related to the assignation of the witnesses.
a. How many witnesses are needed? In the wedding ceremony two witnesses are needed. This is the general rule not only in the case of marriage but also for almost all legal acts (there are very few exceptions where the testimony of one witness is sufficient, for example, aguna). The rabbi who presides over the ceremony is in charge of assigning the witnesses, and he would usually ask the groom to reassign the witnesses he chose “to the exclusion of any other witness.” This is necessary because if someone were to act on his own as an additional eyewitness, and he is unfit to be a witness (for example, a relative of the bride or groom) the entire testimony and the wedding itself will be invalidated. That is why the groom has to assign explicitly the witnesses, usually by saying, atem tihyiu ‘eday, excluding any other person from functioning as an additional witness.