Bede

There are sixty queens, etc. Both queens and concubines indeed approach the king's bed, they bear children for the king, but not both adorn the king's head with a royal diadem. Therefore, both signify souls that adhere to the preaching of truth, and through the word of faith and the fountain of saving baptism, beget spiritual offspring for the eternal king, but there is some, indeed not little, difference of their minds: for queens are those minds that serve the doctrine with the view of the heavenly kingdom. …

Commentary on the Song of Songs ↗

Bonaventure

Solomon represents Christ, except in the women in whom there is no good that can have symbolical meaning. Hence, when it is said in the Canticle: "There are sixty queens, eighty concubines, and maidens without number," this does not refer literally to wives: these women are placed here in a mysterious fashion, and they represent perfect and imperfect souls.

Collations on the Hexaemeron, Collation 14 ↗

Robert of Tombelaine

What is designated by the queens, if not the souls of the saints, who, while they prudently govern their bodies and preside over others, acquire for themselves an eternal kingdom? For there are some in the holy Church who mortify their flesh and afflict it for the sake of God, conquer vices, subject demons to themselves as though tyrants, wisely govern all their impulses so that they run in an orderly manner, preach to others what they themselves do, and fighting with the sword of the word, snatch many from the jaws of demons. …

Commentary on the Song of Songs, Chapter 6 ↗