It's commonly known in Vedic astrology that the Moon represents the mind or manas in Sanskrit. However, in the English language we often make the mistake of equating the mind with the intellect. We say phrases like "Einstein had a brilliant mind," or "I like the way that person's mind works." What we really mean is the intellect, which is our rational, analytical, logical, reasoning power, which is represented by Mercury. Mathematics is also ruled by Mercury.
The mind and the Moon, on the other hand, represent our thoughts, feelings, and perceptions that determine our state of awareness, our relative experience of happiness. It is our psychological conditioning and habitual thought patterns that determine how we perceive the world. The spiritual path could be summarized as "purifying the mind" until only the Divine is perceived at all times, which is a definition of enlightenment.
The tradition of Vedic astrology has always recognized the importance of the Moon for our emotional, psychological, spiritual well-being, which is why it is a lunar-based system, as opposed to Western astrology which is a solar-based system.
In natal chart interpretation we have to separate the mind from intellect to understand the difference between the Moon and Mercury. Both represent distinctly different thinking processes.
- Gautama Buddha, in the Dhammapada