Crystal cord
The crystal cord is the stream of life, or “lifestream,” that descends from the heart of the I AM Presence to the Holy Christ Self to nourish and sustain (through the chakras) the soul and its vehicles of expression in time and space. It is over this “umbilical” cord that the energy of the Presence flows, entering the being of man at the crown and giving impetus for the pulsation of the threefold flame as well as the physical heartbeat. The crystal cord is often referred to as the silver cord because of its silverlike appearance (see Eccles. 12:6).
When a round of the soul’s incarnation in Matter-form is finished, the I AM Presence withdraws the crystal cord, whereupon the threefold flame returns to the level of the Christ, and the soul clothed in the etheric garment gravitates to the highest level of her attainment where she is schooled between embodiments, until her final incarnation when the great law decrees she shall go out no more.
See also
Sources
Jesus and Kuthumi, Prayer and Meditation.
Mark L. Prophet and Elizabeth Clare Prophet, The Path of the Higher Self, volume 1 of the Climb the Highest Mountain® series.