The Song of Songs describes the relationship between a bride and groom, and the Sages explain this as a parable describing the relationship of the Jewish people with their Creator. God is the bridegroom, the beloved, and He searches for His bride, the Jewish people. Every wedding ceremony is attended by the mystical community of Israel that comes from the upper world, and participates in the joy of the bride in this lower world.

One must make the wedding canopy with precious materials in honor of the [heavenly] bride, mentioned in Song of Songs, who attends the celebration of the earthly bride, who symbolizes her. The wedding canopy in which the bride abides is a symbol for the heavenly canopy where the [heavenly] bride is, and it is perfectly beautiful, in a variety of precious shades. For the heavenly and earthly brides are in one image: The former is blessed with seven mystical blessings; seven rivers empty fine oil upon her. The latter is blessed with seven blessings [recited under the canopy] that reflect the seven heavenly blessings. (Rabbi Yeshaya HaLevi Horowitz, Shenei Luĥot HaBerit, Sha’ar HaOtiyot, Kedushat HaZivug)

The Zohar describes how God brings the souls of deceased parents from the Garden of Eden in order to rejoice at the weddings of their children. Earlier generations also come to participate in the celebration.

At the time of the wedding, the souls of the ancestors arrive from the World of Truth, as far as three generations back; this is the case for all of Israel, and there are those for whom [souls come from] even [earlier generations]. (Rabbi Yosef Yitzĥak Schneersohn, Sefer HaMa’amarim Kuntresim 1:38b)

Further reading: For more on relationships, see p. 179; A Concise Guide to the Sages, p. 376.