Although he attached himself primarily to Nankana Sahib, he traveled throughout the Punjab districts preaching the Singh Sabha creed of reformation of Sikh custom and practice. He also espoused the shuddhi movement aimed at proselytizing members of other faiths and of the socalled low classes admitting them as members of the Khalsa brotherhood. Endowed with a good singing voice and equipped with a vast store of knowledge, historical as well as scriptural, Bhai Mul Singh was one of the most popular Sikh preachers of his time. His sermons were laced with quotations from gurbani, the Qur`an, Bhai Gurdas, Diwani Goya, Shaikh Sa`adi and Firdausi.
Bhai Mul Singh was also a versifier of some merit. Four of his works published in his lifetime are extant: TibbiMul, a treatise on Unani system of medicine; Upkar Khalsa, the story of 16,000 Hindu girls taken prisoner by Afghan invaders and rescued and restored to their homes by the Dal Khalsa: Guru Garib Nivdj, a brief history of the Sikhs and denunciation of superstitious rites; and Khalsa Chandan Brichh explaining the anand karaj ceremony in the context of the marriage of Bibi Sahib Kaur, daughter of Bhai Subeg Singh Shahid of Jambar, to a Sikh young man of Garmula Virkan.
The lastmentioned book, published in 1935 gives in the introduction nine other titles "ready for press" and four more "in preparation". It is doubtful if any of these 13 works was ever published. Bhai Mul Singh retired from active life after 1935. He died peacefully at this village home in 1945.
1. Narain Singh, Akali Morche te jhabbar. Delhi, 1967
2. Piar Singh, Teja Singh Samundri. Amritsar, 1975