Genesis 1:19 Kabbalah

וַֽיְהִי־עֶ֥רֶב וַֽיְהִי־בֹ֖קֶר י֥וֹם רְבִיעִֽי׃ (פ)

And there was evening and there was morning, a fourth day.

Read kabbalistic (mystical) interpretation of Genesis 1:19: and classical mystical sources.