This is the melody to which Gurnemanz proclaims,
Gesegnet sei, du Reiner durch das Reine! It is derived from the beheaded Redemption motif (#1D). It accompanies the foot-washing, the blessing of Parsifal, his anointing and the baptism of Kundry.
The first phrase of this theme is similar to Tristan's
O sink' hernieder, Nacht der Liebe.