Could you provide a detailed explanation of the concept of 'Jan-Janardan' and its philosophical underpinnings as discussed in the text?

The provided excerpts from Chapter 0 mention the concept of serving 'Jan-Janardan' in the context of writing a Guru's biography. It states that the writer gains the merit of serving God in humanity (Jan-Janardan). However, the text does not offer a detailed philosophical explanation of this term or its underpinnings. The reference is made in passing to describe a benefit of service, but a deeper exploration of what 'Jan-Janardan' means is not present in this section.