The face of God is the divinity, and the mountains are the soul’s faculties (memory, intellect, and will). This verse is like saying: Let Your divinity shine on my intellect by giving it divine knowledge, and on my will be imparting to it the divine love, and on my memory with the divine possession of glory.
The soul asks in this line for everything she possibly can ask of Him. She is no longer satisfied with the knowledge and communications of the “back” of God - which was His communication to Moses [Ex. 33:23] - and which is knowledge of Him in His effects and works; she can only be satisfied with God’s face, which is an essential communication of the divinity to the soul. This communication is not brought about through any means, but through a certain contact of the soul with the divinity. The Spiritual Canticle, Stanza 19, nbr. 4.