Spiritual Growth

One of the books I am currently reading, The Tibetan Book Of Living And Dying, by Sogyal Rinpoche, makes a big deal out of the importance of having a devotional relationship with some sort of teacher/master/enlightened being/saint/guru, if one is to achieve any sort of advanced spiritual condition.  I have encountered much the same belief in my investigations of other spiritual and religious traditions.  This belief has bothered me some since I have no current earthly teacher or master who is the object of my devotion.  I do receive very clear and precise support and guidance from the Source that I call God, and my devotion to that Source is total.  My teacher/master/enlightened being/saint/guru does not merely represent the Source, for some reason that I do not understand he/she/it is the Source.  That fact scares me and fills me with awe and gratitude.