What is Mandaeism?
Mandaeism is an ancient lifestyle. Its name derives from the Aramaic word, "Manda /ࡌࡀࡍࡃࡀ", which means gnosis (knowledge). According to the Mandaean books, the knowledge of these "knowers" exists as long as humanity. It has also been upgrading over time until the majority of the Mandaean people changed their Mandaic language into Arabic to be able to hide amongst the Arabs, fearing for their lives. 
So Mandaeism started with Adam, the first man:
࡞ ࡀࡃࡀࡌ ࡎࡋࡉࡒ ࡅࡏࡕࡉࡁ ࡏࡋ ࡀࡉࡍࡀ ࡌࡅࡔࡊ ࡅࡀࡌࡀࡓ ࡀࡍࡀ ࡄࡅ ࡌࡀࡋࡊࡀ ࡋࡀࡉࡉࡕ ࡃࡉࡋࡉࡀ ࡀࡍࡀ ࡄࡅ ࡌࡀࡓࡀ ࡊࡅࡋࡇ ࡀࡋࡌࡀ ࡎࡀࡓ ࡁࡊࡅࡋࡇ ࡀࡋࡌࡀ ࡀࡆࡀࡋ ࡅࡀࡎࡌࡀࡊ ࡏࡋ ࡈࡅࡓࡀ ࡄࡀࡉࡆࡀࡊ ࡀࡃࡉࡒ ࡄࡆࡀ ࡏࡋ ࡓࡀࡄࡀࡈࡀ ࡒࡀࡕࡉࡀ ࡌࡍ ࡀࡕࡅࡕࡉࡀ ࡈࡅࡓࡀ ࡄࡀࡉࡆࡀࡊ ࡏࡔࡕࡀࡈࡉࡀ ࡅࡏࡎࡕࡀࡄࡀࡐ ࡏࡋ ࡀࡍࡐࡇ ࡅࡀࡌࡀࡓ ࡋࡀࡉࡉࡕ ࡏࡍࡉࡔ ࡓࡀࡌ ࡌࡉࡍࡀࡉ ࡅࡂࡀࡁࡉࡓ ࡌࡉࡍࡀࡉ ࡄࡀࡆࡉࡍ ࡓࡀࡄࡀࡈࡀ ࡌࡉࡀ ࡄࡉࡉࡀ ࡌࡉࡀ ࡄࡉࡅࡀࡓࡉࡀ ࡀࡋࡌࡀ ࡀࡕࡉࡀ ࡎࡀࡊࡀ ࡅࡌࡉࡍࡉࡀࡍࡀ ࡋࡉࡕࡋࡅࡍ ࡄࡀࡉࡆࡀࡊ ࡏࡑࡓࡇ ࡍࡐࡀࡋ ࡌࡍ ࡎࡀࡌࡊࡇ ࡏࡕࡄࡀࡔࡀࡁ ࡁࡏࡑࡓࡇ ࡅࡀࡌࡀࡓ ࡀࡍࡀ ࡏࡌࡃࡉࡕ ࡋࡀࡉࡉࡕ ࡌࡀࡋࡊࡀ ࡓࡀࡁ ࡌࡉࡍࡀࡉ ࡌࡍ ࡃࡉࡋࡉࡀ ࡄࡀࡔࡕࡀ ࡏࡊࡀ ࡓࡀࡁ ࡌࡉࡍࡀࡉ ࡎـــــࡀ
Adam arose and became arrogant and said, "I am the King without peer, I am Lord of the whole world". He travelled into the whole world and then rested upon a mountain, then he looked and saw a stream that was coming from beneath the Mountain. Then he prostrated and casted himself down upon his face and said, "If there is none loftier than me, and mightier than me, whence comes this stream of living water, of clean water, coming on earth without limit or count?" And so, his thought became disquieted and he pondered in his mind and said "Did I say that there was no king greater than I? Now I know that there exists One who is greater than I am!
Source: The Mandaic scroll: "The great first world /ࡀࡋࡌࡀ ࡓࡉࡔࡀࡉࡀ ࡓࡁࡀ".
This text explains how the first humans discovered the existence of an intelligent being that is more sophisticated than humans, which they call the Life or the Living one (Hai-i /ࡄࡉࡉࡀ). As soon as their ancestors found out about the Life, they recognized the difference between good and evil. Their dualistic philosophy is based on logical thinking and justified behaviour. Thus, this intelligent being, in which all Life started, became labelled as God. The Mandaic God is almighty in the good and in eternity. From his own substance, good entities goes out, which, as soon as they reach their individualization, are tempted by a hostile principle, or evil (Ruha /ࡓࡅࡄࡀ). God does not use evil with which He can oppose the evil. The evil at the other side, is for the Mandaeans, a so-called nothing, which can only manifest itself in temporality. 'It is, and it is nothing.' The evil is not capable of creation. It affects the entities of God to cut them off from their source. With this thought in mind, the Mandaeans initially see the creation of the solar system, including the earth and humanity, as a spiritual disaster. The creator angel (Ptahiel /ࡐࡕࡀࡄࡉࡋ), who received divine orders to create, sinned by an attack of evil and did not fulfil his duties as he should. He created a body in which he has very treacherously attracted part of the divine emanations. 
Therefore, the physical body belongs to the creation of evil, the soul belongs to the Living God, and the spirit is the commitment to the clash between good and evil. For this reason, the Mandaeans will always attach a special importance to a logically thinking soul and a justified handling spirit. This is a mandatory path that enables humans to understand and free themselves from evil. This state of liberation can only be acquired through a harmony between soul and spirit. It could be implicitly understood that every human being has an assignment: to protect the good from an irresistible evil infestation. The Mandaean will only be able to find true freedom by vanquishing evil and resisting it forever. This freedom can be achieved in the course of a very long development process.