What is the exact process of how mantra japa leads the seeker into samadhi?
I know there are many stages you go through and eventually the mantra goes on by it self but would love to read and understand a full breakdown of it.
Sri Sitaramdas Omkarnath quotes from Tantra in His writing বিরহিণীর অভিসার (in Omkarnath Rachanavali, vol 1): मन्त्रसिद्ध्या देवतायां विधाय मनसो लयम्। त्रिपुटिनाशतः योगी समाधिमधिगच्छति॥ मनो मन्त्रस्तथा देवो जायते प्रथमं पृथक्। ततो परस्परं तत्तज्ज्ञाने लीनं प्रजायते॥ क्रमेण मनसो नाशे समाधि किल जायते। समाधिना भवन्त्याशु कृतकृत्यश्च साधकाः॥
By mantrasidhi, dissolving the mind in the devata, the yogi attains samadhi by triputinasha. At first, mind, mantra and devata seems separate. Later mind merges in mantra and mantra in the devata.Gradually mind dies and samadhi is experienced and the aspirant becomes illumined.
According to Sri Sitaramdas Omkarnath, the mantra merges with OM. Whenever the siddha wants to chant the mantra, OM appears and takes the sadhaka to samadhi. His door of sushumna is fully opened.
Hope this answers the question.
His writing have been translated into English. The name of the book is: The Madman's Jholi.