Spiritual Truths is based on a seekers spiritual experiences over one decade. It is based on the teachings and spiritual experiences under Shirdi Sai Baba. It views the Sufi experience from a Hindu perspective.
The Secret Meaning is based on research into the Sufi writings of Mevlana Rumi & other Sufis, as well as the spiritual experiences of a seeker. It views the Sufi experience from a Muslim perspective.
Gurbani Vichar is a detailed review of the Sikh Holy Book, the Shri Guru Granth Sahib (SGGS) from a spiritual perspective. It incorporates both Sufi and Hindu thinking and also covers Sikh history.
All three books are authored by the same person with Book 1 being the earliest and Book 3 being the latest.