This highly sanskritised form of Bengali is notable for its variations in verb forms and the vocabulary which is mainly comprised of Sanskrit words or tatshama words. It was plainly an artificial vocabulary made for the necessity of the literary works at that time. Notably Iswar Chandra Vidyasagar standardised the alphabets and paved the path for literary works. The colloquial usage of Bengali had a vast amount of Persian and Arabic words embedded into the vocabulary, as a result the Sanskrit pundits chose the path of sanskritisation to make a "pure" language which is not to be used in day to day conversation but will be used as a modern representative of classical languages into what the works of Sanskrit literature can be translated.
The development of Sadhu bhasa and Chalit bhasa were more or less a parallel development. By the time Vidyasagar,Bankim Chandra Chattopadhyay are creating the ground work for Sadhu bhasa, Kaliprasanna Singha, Peary Chand Mitra and others are realising the strength of the chalit bhasa.
By the time of Rabindranath Tagore the sadhu (pure) part of Sadhu bhasa has waned into just a set of verb forms. And in a decade or two he himself would choose Chalit bhasa as a literary form of Bengali.