In Christianity's belief, human beings have body, soul, and spirit whereas animals only have the former two. The human kind differs from any other animals, according to the bible, by at least the following three counts:
1) God made man from dust through a special process and made woman from a rib of man;
2) Man was made according to God's image;
3) Man has a spirit, which is the link between man and God, because God is a spirit.
Everyone knows that everyone has a body, which is the material aspect of our being. I would assume no one has any problem with this.
We know that we have knowledge, emotion, will, and the ability to reason. None of them are material but they are real. I would assume most people do not have any problem acknowledging this. They are collectively our soul.
Our body is controlled by our soul. We learn knowledge, take in information, analyze inputs (reasoning), and make decisions. When a decision is made, our will commends our body to take actions.
As biological beings, our decisions are usually rationalized to maximize the benefits to ourselves, sometimes mutually beneficial but mostly at the costs of others. Nevertheless, everyone has the experiences of doing something against one's reasoning, emotion, and will, not to benefit oneself but to benefit others at the costs of one's own or feel guilty about not to do so. That we call conscience and conscience, according to the bible, belongs to the spirit. Furthermore, the spirit links us to God.
If we submit ourselves to the spirit, then we belong to God and will be regarded by God as His beloved children. If we yield to our own will, i.e., the desires of flesh, then we are imprisoned by our sinful nature and are separated from God as a result. The state of being separated from God is spiritual death. Since the flesh does not last long, spiritual death is the real death.
God is the light of life. He is the source of everything good. Wherever absent from God's presence, there is darkness, horror, and suffering. Such places are also called the hell.