What is Ruh'l-Qudus (Holy Spirit) from an Ismaili Point of View?
 
"The Holy Spirit literally means the sacred soul. It is the mazhar (locus of manifestation) of the Divine name quddus (the Holy). Therefore, the Holy Spirit itself is pure and keeps pure from all kinds of uncleanliness all those from whom, according to the Divine command, it manifests in the form of knowledge, wisdom, rectitude and guidance. This is the purport of the verse which is revealed about the pure ahl al-bayt (the Family of the Holy Prophet): "Indeed Allah wishes to remove (all kinds of) uncleanliness from you, O ahl al-bayt, and purify you as ought to be purified." (33:33). Thus the ahl al-bayt are called "Five Holy Persons (panj tan-i pak)" because of this Holy Spirit. The purpose of God keeping them away from all kinds of uncleanliness is to grant them the lofty ranks of heavenly revelation and Divine knowledge and make them the model of mercy and means of guidance for the people of the world."
 

Pir Nasir-i Khusraw and Spirituality, p. 18.

Why is the Holy Imam Distinct and Unique?
 
"The distinction and unique position of the Holy Imam in the world of humanity is due to the Holy Spirit given to him, by which the soul necessarily remains pure. For, the Holy Spirit has all meanings of being pure and purifying. The Holy Spirit rests on the human or rational soul and therefore its center is above the centre of the rational soul, i.e., the forehead, which is the highest place in the human personality and is the place of manifestation of spiritual miracles."
 

What is Soul?, p. 2

What can a True Mu'min get from the Spiritual Treasury of the Holy Imam?
 
"The same sacred light also arises in the forehead of the perfect arif for the sake of recognition. Thus, azal, abad and other realities are gathered together and centered in the enclosure of light of the forehead (of the arif or the true mumin)."
 

A Thousand Wisdoms, Tawil number 13, p.25