Musar for Kiddushin 81:3

We have learned in Kidushin 41: The commandment to be מקדש את האשה devolves first and foremost on the actual groom, though it may be performed by anyone he designates. When the Jewish people left Egypt, G–d (the groom) personally performed the act of קדושין: The Torah says of G–d: ועברתי בארץ מצרים (Exodus 12,12). The ceremony was, however, also performed by a messenger whom G–d had designated, viz: וישלח מלאך ויוציאני, "He sent an angel (messenger) and took me out" (Numbers 20,16). The actual wedding ceremony, the נישואין, must be carried out by the groom personally, not a stand-in. The giving of the Torah at Mount Sinai symbolised this wedding ceremony between G–d and the Jewish people. This wedding took place on the Sabbath, an occasion when G–d spoke to Israel פנים בפנים דבר ה' עמכם, "Face to face did G–d speak with you" (Deut. 5,4). The usual time for man and his wife to join conjugally is on the Sabbath. This is part of the mystical aspect of marriage.