The Spirit
Our material or physical body that contains flesh and bones is not the real "man" rather this physical body which is composed by muscles, tissues, flesh and bones is merely a cloak of the "real man" in it. Just as clothes of wool, leather or cotton are used for the protection of this physical body similarly this physical body is an attire of the "Spirit"; "the real man" as called by the Almighty God.
The Spirit has its own gradations. Due to lack of knowledge, usually the soul is considered to be a human being just like the one which we see in the form of physical body of flesh and bones. Spirit is such a reality which is an indivisible entity, self-subsisting and unwaveringly related and established only with its own self. It has this unique quality of demonstrating itself in a variety of forms and shapes remaining perpetually kinetic and subsisting. It is one of its main characteristics that it never exhibits itself in hypothetical and fictional senses, though it uses them as its robe. But since to remain perpetually kinetic is one of its attributes therefore it makes itself manifested in various dresses. Sometimes its manifestation is in the form of a goat, sometimes it expresses itself as a cow, sometimes it is a jinn and at times the angels.
Now the question is that, what the Spirit is, and how does it exist? To find out the answer, we have to look at God's last revelation, the Last Holy Book of God, the Quran.
"They ask you (Prophet Mohammad) concerning the Soul, say: The Spirit is by my Lord's Determination, and of knowledge you (mankind) have been given only a little (Quran 17:85)"
In the above verse God says that the Spirit is His Determination. Now another question comes into our minds that what is God's Determination? To find out it's answer, we have to look again the Holy Quran:
"Glory be to Him (God), when He Determines , He only say "Be" and it is. (Quran 19:36)"
So, God's determination is that when He Determines, He just say "Be" and it would be done instantly. It means that Spirit is God's manifestation. Spirit is the only source for us to contact God. It means that by contacting to our soul, we clear our way to be closer to God.
As we look after our physical body, take care of its requirements, cleanliness, want to look physically good etc. In the same way it is also necessary to look after our Spiritual Body, our Spirit, to take care of its requirements & cleanliness.
Now the point is that what is the requirement of our Soul, and how should we take care of the cleanliness of our Soul? Our Soul's only requirement is that we should not be careless & ignorant about our spiritiual existence. We can take care of the cleanliness of our Soul by not having any kind of negative feelings & emotions into our heart, be kind to others, and always search for our innerself.
The Last Prophet Mohammad said: "The person, who cognized himself, he cognized God."
We can only cognize ourself by cognizing our real existence, the Spirit. Tasawwuf or Sufism provides us a way to cognize ourself, teaches us about our real self (The Spirit), and takes us closer to God.