The Mishna (50a) teaches that if a yavam (the surviving brother) first performs ma’amar (see daf 51) – offering a ring or another object of value to the yevama (widow) as though he were marrying her – and then performs normal yibum by engaging in sexual relations with the yevama, he has fulfilled the mitzva appropriately. The Gemara on our daf explains that this appears to support the teaching of Rav Huna, who recommends that a yavam should not simply sleep with the yevama, but rather he should treat the relationship as one that is similar to marriage, beginning with a formal agreement, and only afterwards consummating the marriage with a private, personal act.
In support of this idea, the Gemara brings the ruling of Rav who would punish people who agreed to have kiddushin – the first act of marriage – by means of a sexual encounter, even though this is one of the three methods of which the Mishna (see Kiddushin 2a) approves. (The other two are kesef – money, or as tradition has it, a ring; and shtar – a legal document.) Similarly, Rav punished people who agreed to kiddushin in the marketplace or without a properly arranged shiddukh.
The reason behind all of Rav’s punishments – as well as Rav Huna’s ruling with regard to yibum – is that, notwithstanding the letter of the law which permits a sexual act to solidify a marriage agreement, such behavior shows a lack of respect for privacy and modesty, which are the very foundations of marriage. Furthermore, agreeing to marry when standing in the marketplace or without proper preparations indicates that this is seen as happenstance and is reminiscent of a “one-night stand” rather than a true marriage.
The idea of shiddukh that appears in the Gemara is originally an Aramaic word whose meaning appears to be “to calm” or “to quiet.” In its borrowed form, it has come to mean to appease or to placate; to persuade. In our context, it indicates an agreement between the man and woman or between their families prior to marriage.