L’kovod the Blass Aufrauf
The minhag to throw candies and the like at, or in front of, the chosson on the Shabbos before the wedding, as he gets his Aliyah, is a common minhag brought in Shulchan Aruch. It is a sign of joy, berachah, and simchah.
Medrash Talpiyos (Anaf Chasan V’kallah) says that the reason that he gets an Aliyah on the Shabbos before his wedding is because “chasan domeh l’melech” – a groom is compared to a king, and a king must have two sifrei Torah, so too a chasan gets one Aliyah before and one Aliyah after his wedding. Rav Shlomo Zalman in Halichos Shlomo (Moadim 2:251-252) offers an idea based on the Gemara Nedarim, which says that the reason that the Beis Hamikdash was destroyed is because we did not have proper kavod hatorah. So, the greatest way to give proper kavod hatorah is to learn right before an important time in our lives. Therefore, prior to his wedding, the chasan gets an Aliyah and starts his simcha off with Torah. Sifrey Chabad say that it is a siman tov for raising children who will learn Torah and lift up the world. Sefer Hamatamim quoted in Nitey Gavriel (Hilchos Nisuin) writes that the reason that a chasan gets one Aliyah before and after his wedding is in order that he appreciate the difference between the Torah learned before and after his wedding. Chazal tell us that “hasharuy b’lo isha , sharuy b’lo Torah”. The Torah he learns has new meaning when he is married.