Instructions by a spiritual teacher (Guru) on what one should do with their life while on the path that leads them back home, back to Godhead, can be different for each individual based on time, place, circumstance, commitments and personal realizations.

It is nonsense to think every devotee and aspiring devotee should never study the origin of the material creation, and learn its history, origins and destination, just because Prabhupada told one devotee to ONLY chant Hare Krishna, serve in the Temple and not bother studying the structure of material creation.

Yes, even though such instructions ARE valid, Prabhupada's instructions ARE different for other devotees too that are also mentioned in his lectures, morning walks and letters.

In other words, Prabhupada gives different instructions to his followers based on what THEY each can offer in service.

Many seekers of truth want to learn the vast knowledge of the Vedas therefore, it is necessary that there are devotees who can accurately pass on that knowledge and that is why Prabhupada wrote so many Books.

Therefore we must understand that personal letters, conversations like morning walks and room discussions by Prabhupada, are often meant for a particular person or devotee according to time, place and circumstance suitable for their personal realizations and intelligence.

Prabhupada gave many different instructions to devotees and aspiring devotees that helps them advance according to their realizations and what is best for them.

Some devotees are natural preachers and need to learn historical events and pastimes of both the perpetual Spiritual realm and the temporary material creation so they can teach others who inquire with their preaching.

So it is a fact, Prabhupada said many things to different individuals according to their realization that included studying the structure of the material universe found in Srimad Bhagavatam.

Why do you think Prabhupada translated ten Cantos of Vedic text Srimad Bhagavatam that includes the explanation of the structure of the material creation in detail? 

Prabhupada told us to study and learn his Books and also find other Books like Surya Siddhanta by Srila Bhaktisiddhanta Sarasvati Thakur and study.

The understanding is wrong that all Prabhupada's letters and conversations can be applied to everyone, no, that is not true.

In fact, many devotees are meant to learn BOTH at the same time-

1 - Study the nature of this material creation by reading Prabhupada's Books. 

2 - And go back home, back to Godhead via the process of chanting the Hare Krishna Maha-Mantra and street Sankirtan.

Prabhupada encouraged both hand in hand.

Once again, Prabhupada wrote so many wonderful Books full of knowledge about both the material creation and the Spiritual Worlds.

He told us to learn both.

But ultimately the most important activity one should ALWAYS do is chant Hare Krishna.

Lord Caitanya Mahāprabhu once asked the great devotee Ramananda Raya-

 "Among all that is worshipable which is the chief or most important?"

Rāmānanda Rāya replied - "The chief worshipable object is the holy name of Rādhā and Kṛṣṇa, the Hare Kṛṣṇa mantra."

The Śrīmad-Bhāgavatam further confirms this-

etāvān eva loke 'smin puṁsāṁ dharmaḥ paraḥ smṛtaḥ

bhakti-yogo bhagavati tan-nāma-grahaṇādibhiḥ

"In this material world the living entity's ONLY business is to accept the path of bhakti-yoga and chant the holy name of the Lord." (Srimad Bhagavatam Canto 6 Chapter 3 text 22)^^*