There are threescore queens, and fourscore concubines, and virgins without number.
Read Chapter 6
In the present verse, therefore, three orders of merit are indicated to be in the church according to the following enigma. First, clearly, there are teachers, living an immaculate life. Second, there are the teachable, who imitate the lives of their teachers and burn with great desire to understand the content of the teaching and to distinguish sound doctrine from unsound doctrine. But the third order is that of maidens, for whom only belief in the one God helps toward salvation, who are not yet worthy to be joined to the sacred number. Although all of them may have the Word of the Father as King, he who was with the Father in the beginning and always remains God in the Father, the dignity of merit nevertheless escapes them. - "Exposition of Song of Songs 9.21"
queens are those who devote themselves to the teachings of the kingdom of heaven.
Concubines are those who proclaim Christ along with love for worldly things.
Maidens without number are those who devote themselves to obey the commandments though they are not teachers or preachers. (St. Bede)
The word queens refers to the souls that rule in the realm of the intelligible and spiritual. The word concubines [refers] to the souls that receive an earthly reward, concerning whom it is said, “They have received their reward.” - "On Eighty-three Varied Questions 55"