The difference between sakara and nirakara is the same as the difference between ice and water

 The principle of Easwara has two aspects. One is Saguna Sakara (attributeful and formful) and the other is Nirguna Nirakara (attributeless and formless). Associated with the mind and thoughts, and responding to the joys and sorrows, the pain and sufferings of human beings, various forms of Divinity have been visualised. These are the Saguna and Sakara aspects of Easwara. In this context, we have the Trinity - Brahma, Vishnu and Maheswara. These are associated with the three Gunas or attributes - Rajas, Sattva and Tamas. Rajas is associated with Brahma, Satva with Vishnu and Tamas with Shiva. Brahma is represented by the sound 'A'. The sound 'U' is the manifested form of Vishnu. And 'M' is the form of the Shiva principle. These three forms are not permanent, because anything which has a form cannot be permanent. These physical forms are forms of delusion, the result of thoughts, the expressions of mental tendencies. But there is one syllable consisting of 'A', 'U' and 'M', which is the One underlying all the three forms - that is the Omkara. Whatever number of births we may take and however long we may go on worshipping these three forms, we will never be able to free ourselves from the cycle of birth and death. If one wants to get rid of birth forever, one has to worship the Nirguna Nirakara, the formless and attributeless principle, which is represented by the Omkara.

Bagavan Sri Sri Sri Sathya Sai Baba