On a surface level, the mental body is your thoughts. On a deeper level, it is the domain of your beliefs, desires, values, and goals. Beliefs are opinions and convictions that we hold as being true without having immediate proof. Values represent what we hold internally as most important in an area of life. Values and beliefs can come from thoughts that were formed very early in childhood.
We all have desires to achieve or acquire something in our lives, which is why we set goals and intentions to help us get where we want to go. Some surface-level thoughts, which may create goals or desires, direct our mental focus from moment to moment. This is how our logical, linear minds learn and operate, and it is one of the aspects of ourselves that is most familiar to us.
The spiritual body is your connection to energy. For some, this may be more closely tied to religion than spirituality. For others, it could have more to do with the atoms in the body or the quantum energy that science refers to. Whichever way you choose to view the source of your energy is perfect.
To fully access the spiritual aspect of your being, maintain a daily practice that keeps this connection open. If a blockage occurs, energy and information are unable to flow freely from the spiritual body down through the mental, emotional, and physical bodies. This is why a daily spiritual or religious practice is so important to maintain this open connection. To be in a state of harmony between each of the layers of our being, we need to develop our intuition and spirituality as much as we do our mind and emotions to create a solid physical foundation.