Sahajayana a reformed form of mahayana Buddhism which developed between the 8th and 12th centuries. Its basic philosophy was to seek nirvana by leading a life under a chosen guru rather than by undergoing hard devotional practices. According to the Sahajayana concept, nirvana can only be attained through a vrajaguru, that is, a guru devoid of vraja or desire. Supreme bliss, according to Sahajayana, is achieved through the union of man and woman. The body here is regarded as the field of devotion.
According to the followers of this concept, the world is void, nirvana is void and there is no such thing as sin or virtue. Since everything is void, nothing is created and nothing destroyed. Even the mind is void. This emptiness of mind is eternal bliss or nirvana. All pain ends in nirvana and the ultimate result is bliss.
According to this cult, it is unnecessary and futile to attempt to control the senses or follow ascetic rites. This merely brings bodily pain and disturbs one's peace of mind, without which nothing can be achieved. According to the Sahajayana concept, one need not go through pain of worship; rather one should seek bliss through enjoyment. According to its followers, one should enjoy the five senses, subject to the permission of the guru. Those who do not enjoy the five desires cannot achieve nirvana.
This Sahajayana philosophy at one time spread widely in Bengal. The vrajagurus also approved whatever the followers wanted. This is why the vrajagurus were also known as siddhacharyas. The siddhacharyas used to explain the scriptures and give lectures and sermons. They also used to sing songs in a variety of ragas to spread their philosophy. The language of these songs was known as sandhya bhasa or twilight language as it was understood only partially. This twilight language is the earliest specimen of bangla language. This is why the earliest siddhacharya, Lui, is known as the earliest poet of bangla literature. The collective composition of the 84 sahajiya siddhacharyas is called charyapada. This is the earliest book of Bangla language and literature. [Suman Kanti Barua]