A kabbalistic manual preserved in Kitzur Shalah (an abridgment of the early seventeenth century ethical-mystical work Shenei Luchot HaBrit by Rabbi Isaiah Horowitz) describes the proper way for a person to immerse himself in the mikveh, the ritual bath, on a day of deep penitence.
The instruction is precise. The person must stoop four times while standing in the water, each stoop deep enough that the water reaches his neck. These four immersions correspond to the four forms of court-imposed capital punishment described in the Mishnah: stoning, burning, beheading, and strangulation. The immerser, in other words, symbolically accepts a fourfold death in the water, so that the living body emerging is as one already acquitted.
After the four stoops, he recites the traditional confession. Then, with the water still touching his throat, he speaks three verses, one for each aspect of divine mercy. Who is a God like unto Thee, pardoning iniquity (Micah 7:18-20). O Lord, correct me, but in measure (Jeremiah 10:24). I called upon the Lord in distress; the Lord answered me and set me in a large place (Psalms 118:5).
Then comes the formula itself: As I cleanse my body here below, formed of clay, may the ministering angels cleanse my soul, spirit, and ghost above in the river Dinor (the River of Fire). And as I sanctify my body here below, may the angels of the Most High sanctify my spirit, soul, and ghost in the river Dinor above. In the Name of the Holy One, He is God, and in the Name of Adonai, the Rock of all ages. Blessed be the Name of the glory of His kingdom forever.
This passage, preserved in Harris's 1901 Hebraic Literature, teaches that every immersion is twofold. What the body does in water below, the soul does in fire above. The mikveh is a mirror of the heavenly Nahar Dinor, the river that flows from beneath the divine throne.