Courtesy - Swami Chimayanand 
Swami ji gave this beautiful example:
The cloud formation is due to evaporation of water from the earth. The rain water is thus distilled water. Rain when falls on the mountains forms small rivulets, which together forms river and then different rivers goes down into the sea. If a water sample is taken from different rivers and rivulets, it is found that every water sample has different composition of mica, calcium, magnesium etc into it depending upto the area which they crosses and thus carry away the property of that area. So the original water i.e. rain water was distilled and pure but it goes on adding different elements as it passes away on earth.
The impurities of river water can be removed if it is boiled and distilled making it the same pure rain water as before.
In the same way, GOD has created a pure consciousness. Due to karma done in various births (which nobody remembers), Man had carried away with him various different properties of lust, anger etc. So, man consists of pure atman and good and bad vasanas. The vasanas can be removed on the seat of meditation. After the removal of all the vasanas the man will be a pure consiousness which will be freed from painful births and deaths cycle.
Thus MAN has created evil and not GOD which himself is perfect and HE always make perfect things. This universe has evolved from HIM and thus we all were perfect in the beginning but we all has lost our identity during various births.
Meditation is the method to realise the pure ATMAN.
