The Source for Sending Sivloinus
The Sivloinus that Eliezer Gave to Rivkah: We find that Eliezer the servant of Avraham gave sivloinus to Rivkah twice. Once on the way (Bereishis 24:22):ויקח האיש נזם זהב בקע משקלו וגו' – “And the man took a golden necklace of great weight, etc.”, and once when she was in her parents’ house (Bereishis 24:53): ויוצא העבד כלי כסף וכלי זהב ובגדים ויתן לרבקה – “And the servant brought out silver and gold jewelry and clothing and gave them to Rivkah.” Rabbeinu Bechayah (there, and in Kad HaKemech, Inyan Chosan B’Beis HaKnesses) speaks out at length that all the presents and the fact that they were given twice, came to allude to the Torah and the mitzvos that her sons would later accept.
It is clear from the Lekach-Tov (cited in Toras Shlomah), that the minhag for a chosan to send gifts to his kallah before the wedding comes from here.
The Chizkuni (24:53) writes: The first set of gifts that Eliezer sent were gifts after shidduchim, and the second set of gifts were to serve as kesef kiddushin [money for the act of kiddushin], and they followed the custom of מסבלי והדר מקדשי – first send gifts and then perform kiddushin.
Besides for sending to Rivkah, כלי כסף וכלי זהב ובגדים – “silver and gold jewelry and clothing”, which are the sivloinus in Maseches Kiddushin which are given to the kallah, we also find that he sent, ומגדנת נתן לאחיה ולאמה – “pleasant foods he gave to her brothers and her mother” (Bereishis 24:53). Rashi explains that he gave fruit of Eretz Yisrael which he brought with him. However, the Targum Yonasan ben Uziel interprets it as 'ודורונין' which means presents. These were like the sivloinus of Bava Basra, that are sent to the kallah’s house.
The Sivloinus that Hashem Gave to Klal Yisrael: The sefer HaMata’amim (המטעמים) writes that some have the minhag to send sivloinus from the chosan to the kallah in remembrance of the gifts that Hashem gave to Klal Yisrael before giving them the Torah. Before receiving the Torah, Klal Yisrael were given spoils from Mitzrayim, spoils from the sea, the mon, a special well and quail. Many customs that we do for a chosan and kallah are based on what happened at Matan Torah, therefore, since before Matan Torah we received lots of gifts, we do the same thing by a chosan and kallah.
