Man Alone Joins Heaven and Earth

In Derech Hashem the Ramchal explains that all of creation divides into two realms, physical and spiritual. Whatever we can sense, in the heavens and on earth, is physical. The spiritual is whatever cannot be detected physically, namely souls and transcendental beings, which include the Forces and the angels. Of all things, only man is made of two absolute opposites, a spiritual soul and a physical body. Animals have a soul, but not a spiritual one. Everything in this world has its roots among the Forces above, and every process in nature is overseen by some angel. The one exception is man's free will. Hashem willed that man choose freely between good and bad, and so gave him the power to influence the world in any direction he chooses. Since our knowledge of spiritual things lies beyond our experience, we must rely on the traditions handed down to us.