At Mount Sinai, God officially proposed to Israel (so to speak) offering to make them His people if only they would obey Him and keep His covenant. The rabbis compared it to a betrothal. In that metaphor, the Holy One, blessed be He, came to Israel as a suitor proposing marriage to His beloved.
The Almighty was the bridegroom. Israel was the bride. The Torah was their wedding contract (ketubah). Moses played the role of the “friend of the bridegroom” as a liaison between God and the people.
In Jewish wedding customs, the friend of the bridegroom served as an intermediary between the suitor and the woman. In the wedding, he presented the bride to the groom. As the friend of the bridegroom, Moses was responsible for negotiating the match. He brought the bridegroom’s proposal to the girl, and he carried messages back and forth between the two parties.
Finally, Moses led the people to the foot of the mountain and presented them to God:
And Moses went forth and came to the camp of the sons of Israel, and he aroused the children of Israel from their sleep, saying to them, “Arise from your sleep, for behold, your God desires to give the Torah to you. Already the bridegroom wishes to lead the bride and to enter the bridal chamber.” … And the Holy One, blessed be He, also went forth to meet them like a bridegroom who goes forth to meet the bride. So the Holy One, blessed be He, went forth to meet them to give them the Torah. (Pirkei deRabbi Eliezer 41)
In the Gospels, John the Immerser played a similar role. Once, his disciples came to him, warning him that Yeshua of Nazareth was growing in popularity and that His disciples were baptizing people. John’s disciples felt as if Yeshua’s ministry infringed upon their ministry. John corrected them, pointing out that he only came as the forerunner of Messiah. Just as the friend of the bridegroom gets out of the way, relinquishing the girl under his charge to the groom, so too, John needed to relinquish his ministry to Yeshua. John seems to have alluded back to the story of Moses at Mount Sinai by comparing the people of Israel to a bride, Yeshua to a groom, and himself to a friend of the bridegroom:
John answered and said, “A man can receive nothing unless it has been given him from heaven. You yourselves are my witnesses that I said, ‘I am not the Messiah,’ but, ‘I have been sent ahead of Him.’ He who has the bride is the bridegroom; but the friend of the bridegroom, who stands and hears him, rejoices greatly because of the bridegroom’s voice. So this joy of mine has been made full. He must increase, but I must decrease.” (John 3:27-30
Taken from First Fruits of Zion commentary.