Shankara was a well know revivalist who brought Vedanta back to the fore and reestablished a monastic tradition in India. But then the pendulum continued to swing and it came to be understood that withdrawal from the world was necessary for real spiritual progress. Renunciation became the way, partly because of the dark age.
To put this in a larger context, in Vedic philosophy of dharma, our lifespan is divided into 4 sections:
Study, Work and Family (Householder), Retirement, and Sannyasa.
In the last, Sannyasa, we retire from the world and focus on spiritual life- around age 70-75. As an option, young students could skip the householder stages and live a lifetime as a Sannyasi(ni) monk. In some teachings this became the only way.
There are certainly texts that can be quoted to support this position. One is by Shankara himself. He said that you have to take Sannyasa (vows) to get the Mahavakyas, the keys to full enlightenment.
But if we look closer, another understanding arises. The term Sannyasa means to abandon everything. In Self Realization, we shift from being a me identified with the world to being the cosmic witness, observer of the world. We detach from it and experience separation from the world.
Fully established, the attachments to the world have wound down. We have abandoned everything that was “mine” and taken Sannyasa. We then become qualified for the Mahavakyas. But this doesn’t mean we have to leave the world at all – we can be in the world but not possessed by it.
In other words, Shankara may have been referring to an inner stage of development rather than some outer behavior.
This can be further corroborated using the first 2 verses of Chapter 6 of the Bhagavad Gita (6v1-2):
The Blessed Lord said:
He who performs actions which ought to be done,
without depending on the fruit of action,
he is a sannyasi and he is a yogi;
not he who is without fire and without activity.
That which they call Sannyasa,
know it to be Yoga, O son of Pandu,
for no one becomes a yogi who has not
relinquished the incentive of desire.
Notice some key points here. ‘He who is without fire’ refers to a renunciate as they renounce cooking fire too. Krishna is saying a renunciate who abstains from activity is Not a sannyasi unless they are in Yoga. Yoga is the observer established in their own nature – again, the witness. ‘relinquished the incentive of desire’ is another reference to the fruits (results) of action. Non-Attachment is not something you practice; it results from Self Realization.
How you are in the world is of much more significance than what role you play.