Why Sathya Sai Baba insisted on service (seva) in Prashanti Nilayam, Puttaparthi?

Bhagavan Sri Sathya Sai Baba was famous for his insistence on worshipful service to fellow man/woman (Manava Seva is Madhava Seva) as the main spiritual sadhana (practise/discipline) to be followed for all those who came to him. Yes, Namasmarna (devotional chanting/ remembrance of the name of the Lord) and Bhajan (devotional songs/singing), were important too, but his advice was that most of one's time must be spent in service activities, singing bhajans while doing the work, if feasible, or even silently chanting the name of the Lord, if feasible. For Kali Yuga, this was the best spiritual practise according to Swami, the Kali Yuga Avatar.

Today's thought for the day in Prashanti Nilayam ashram throws some further light on why Swami insisted on service for all who came to Prashanti Nilayam (Puttaparthi):

You have worked very hard in your life discharging worldly duties and come to Prasanthi Nilayam, seeking rest for the body and peace for the mind. That being so, it might look strange if you were asked to undertake some kind of work here also. In the olden days the Guru would collect his disciples in the forest and give them different types of work, sometimes for 10 to 12 years. This was done with a purpose. One important object of work is purification of the Chittha (heart). Once the heart is purified one is ready to receive the teachings of the Guru. Therefore in earlier times the disciples were given work in the beginning so that they slowly get purified. Only when the teacher was satisfied regarding the student's ripeness for receiving spiritual instruction, would he start teaching Brahma Vidya (the supreme knowledge). (Divine Discourse, 7Jul 1985)

From: http://www.radiosai.org/pages/calthought2.asp?mydate=2/8/2015

I think the above message has helped very much to improve my understanding of why Swami insisted on service activities, and also given me vital background information on how Gurus of the past ages would train/discipline spiritual aspirants who came to them. 10 to 12 years of service to the Guru/ashram as a process of Chitta shuddhi (purification of heart/mind OR inculcation of right attitude as a spiritual aspirant/student) before Brahma Vidya was taught to newcomer spiritual aspirants! Well, spiritual knowledge (Brahma Vidya), was and, IMHO, typically still is, not for the faint hearted or quick results oriented person. Shraddha and Saburi i.e. faith and patience, as Bhagavan Sri Shirdi Sai Baba would say, are the vital attributes to inculcate and foster, for the spiritual person.