וַֽיְהִי֙ כִּֽי־הֵחֵ֣ל הָֽאָדָ֔ם לָרֹ֖ב עַל־פְּנֵ֣י הָֽאֲדָמָ֑ה וּבָנ֖וֹת יֻלְּד֥וּ לָהֶֽם׃
And it came to pass, when men began to multiply on the face of the earth, and daughters were born unto them,
Read kabbalistic (mystical) interpretation of Genesis 6:1: and classical mystical sources.