What is Guru service and how should it be performed according to the teachings mentioned in the preface?

Guru service is described as a vital path to gaining spiritual knowledge. As quoted in Chapter 0 from Lord Samarth Sadguru Dnyaneshwar Maharaj, one should serve the saints with their entire being—body, mind, and soul—and without ego to have doubts dispelled and the heart enlightened. The preface explains that the means of Guru service are infinite. One form of this service is writing biographies, which can be of worldly figures or of saints. However, the highest form of written service is to write the biography of one's own Sadguru with a pure heart and unwavering devotion, and to study it regularly.