Moses Hayyim Luzzatto, Qin’at ha-Shem Seva’ot, p. 115

Jewish Mysticism
The secret of the matter is that Malkhut in her aspect below is in the secret of the seventh. When she unites with Yesod in the secret of the copulation he himself becomes the seventh since she is a crown on his head. Therefore [he is] the seventh because he is the the sixth that is crowned by the seventh. From his own side he is a waw, but on account of Malkhut who is joined to him he is called the seventh. He is the secret of a waw and the yod is upon him, which is the seventh. Then, on account of his name, the Shekhinah is called sedeq because he is the saddiq.

Translated by Elliot Wolfson in “Tiqqun ha-Shekhinah- Redemption and the Overcoming of Gender Dimorphism in the Messianic Kabbalah of Moses Hayyim Luzzatto,” History of Religions 36 (1997) 289-332.