There are two, and only two, realms … physical and spiritual. These are referred to in the Bible with different words, among them are good and evil, or light and darkness. Often used in the New Testament are the terms flesh and Spirit. The word Spirit with a capital “S” is usually a reference to the Holy Spirit, especially in the New Testament.
Whatever the terminology, the two realms are always the physical and the spiritual. In other words, they are either known to us by our five senses, and as such are physical; or we are aware of them by the eyes and ears of our heart, and are therefore spiritual. Let me note that in Biblical terminology the word heart can be a reference to the organ that pumps blood through our body, or it can mean one’s spiritual nature … the part of us that is spiritual. Another way to describe our spiritual heart is that it is our center or core, the essence of who we are … it is the home of our character and personality. In short, it is not what we look like, it is who and what we are.
Flesh and Spirit represent two kingdoms. Flesh is the kingdom of the physical, Spirit of the spiritual. Satan rules the physical kingdom, God is ruler over the spiritual. The natures of these realms are total opposites … counterparts. The realm of the flesh, as Satan’s realm, is characterized by all that is said to be evil. Included are things such as lying, hating, stealing, murder, greed, deceitfulness, etc. The realm of the Spirit, as God’s realm, is distinguished by all that is good. These include love, joy, peace, forgiveness, unselfishness and the like. Each can be thought of as being the personification of the head of the realm, i.e., of Satan for the flesh, or God for the Spirit.
You should be clear that as you read, study and meditate on passages of the Bible, these two realms are the only realms being discussed. When they are not mentioned explicitly, they are indicated by comparison, metaphor, simile or parable.