I've long been interested in the overlap between psychology and spirituality. The similarities in the two fields are reflected in how readily the psychological community has embraced Buddhist practices such as mindfulness as legitimate means for improving mental health. (I think the Buddhists were way ahead of us on that one -- they realized centuries ago that inner peace is something that is both spiritual and psychological in nature).
Even the meanings of the terms "spiritual" and "psychological" overlap. "Spiritual" is a word with multiple meanings, both objective and subjective. When a person describes himself as spiritual we usually have to ask him to clarify what he means by this, as the word tends to have different connotations for every individual person. To one person spiritual might mean, "of, from, or pertaining to God." In this case, when he describes himself as spiritual he is referring to his relationship with God or some other diety. Some who call themselves spiritual speak to their relationship with nature. In this instance they may be referring to the intangible "spirit" that is inherent in all things natural. In consulting the dictionary I found that both of these meanings are correct. I also found that spiritual can be defined as "of or relating to the mind or intellect." This definition suggests that spiritual and mental are one and the same.
This is, in fact, very consistent with what the Buddhists believe. They believe that consciousness is the essence of the universe and that we can experience our essence through mindful awareness (attention). (I do realize this description is in no way a complete representation of the Buddhist belief system. I'm just keeping it simple; a full description of Buddhist traditions is beyond the scope of this post).
What about psychology? The dictionary defines psychological as "of, pertaining to, dealing with, or affecting the mind, especially as a function of awareness, feeling, or motivation."
So how do psychology and spirituality overlap? At the very least we can say that both fields deal with the mind to some extent. Both also deal with awareness, although perhaps not always in the same way. It seems to me that both disciplines seek to answer the question "Who am I?" and that they both seek to help people find happiness and inner peace.
I hope to write more on this topic but for now I think I've said enough:-)