The letter Kaf stands for "devotion/sincerity" (Kavannah), for "glory" (Kevod), and for "crown" (Keter). Through the crown of our heads a spiritual thread of light enters that fills us with Kavannah and spiritual life.
"Holy, holy, holy, is the Lord of hosts; the whole earth is full of His glory. -Isaiah 6:3"
"Where shall I go from your spirit? Where shall I flee from your presence? If I ascend up to heaven, you are there! If I make my bed in Sheol, behold, you are there! If I take the wings of the morning, and dwell in the uttermost parts of the sea, Even there shall your hand lead me, and your right hand shall hold me. -Psalm 139:7-10"
"Whenever the Torah is studied by night, a little thread of this hidden light steals down and plays upon them that are absorbed in their study. -Zohar II, 7149a"