What is Śāstra?
This question is the first topic of Jīva Gosvāmī’s Ṣaḍ-sandarbha. I’ll summarize and include a concept or two borrowed also from Nāma Cintāmaṇī of Kānupriya Govāmī.
Śāstra is valid-knowledge, which in Sanskrit is called veda. Veda is embedded within creation itself from the source of creation, Viṣṇu. Thus a great deal of knowledge comes automatically, instinctually (as in, how to balance, how to regulate heart beat, how to repair wounds, how to grow, how to breathe, how to mate, etc.). But the more complex knowledge available mainly to species beginning with human beings is not imposed by instinct but is available only to those who want it and seek it.
Brahmā is the first seeker and realizer of the higher knowledge embedded by Viṣṇu in the universe. He explains what he realizes in words, and those words constitute the verbal “Veda.”
Gradually, Brahmā’s veda becomes confusing to people, and as Dvāpara Yuga advances it becomes almost completely messed up. Therefore towards the end of every Dvāpara Yuga, someone fills the role of “Vyāsa” (Editor) and recompiles Brahmā’s veda.
The main topic of the Veda is “Sacrifice” — how to live in such a way as to not be “sinful” or “evil” yet also achieve what you want to achieve. There are four parts to Sacrifice, so the Vyāsa’s create four books about Sacrifice, Ṛg, Yajur, Sāma and Atharva.
Then Vyāsa and his followers compile elaborations on the four Vedas, consisting of the parts of Brahmā’s Veda which are not directly about sacrifice. These mainly become known as the Upaṇiṣads.
But a special section is compiled which is easy to read, speak, and understand, but which contains all the knowledge of Brahmā’s veda completely (Pūrṇam), this section is called the Purāṇa, sometimes known as the “Fifth Veda.”
There are 18 major Purāṇa compiled by Vyāsa. They are superior to the Upaṇiṣad’s and Veda because (a) everyone can relatively easily access them, and (b) the Vedas and upaniṣads quickly become degraded and large portions of them disappear immediately as Kali Yuga arrives.
Of the Puāṇa, 6 are primarily directed towards those with tamasic inclinations, 6 for those with rajasic, and 6 for those with sattvik. The most sattvik is the Bhāgavata-Purāṇa.
This Bhāgavata Purāṇa is a prototype of the Śrīmad Bhāgavatam, it is not the full Śrīmad Bhāgavatam.
In some Dvapara-Yugas, such as this one, rarely (once in 1000), Krishna himself appears, so the Vyāsa feels a special impetus to create an appropriate Śāstric compilation to serve his appearance. After consulting with Nārada and achieving a special samādhi under his inspiration, Vyāsa then recompiles the Bhāgavata Purāṇa, which becomes known as Śrī Bhāgavata / Śrīmad Bhāgavatam.
The Śrīmad Bhāgavatam is the highest form of all Brahmā’s original revelations, and in fact is even higher than the original, because the Vyāsa who compiles it (Kṛṣṇa Dvaipayaṇa) is a śaktyāveśa avatāra of Viṣṇu, and the speaker Śuka, is uniquely realized.
Vyāsa teaches the essence of Śrī Bhāgavata to his son, Śuka. Śuka uses it to answer all of Parīkṣit Mahārāja’s questions. Sūta is present there, and recounts it to answer the questions of Śaunaka and the Naimiṣāraṇya Ṛṣis. This is the form of Śrī Bhāgavata we have today.
No one except Viṣṇu, Brahmā, and Vyāsa writes śāstra. Actually, no one but Viṣṇu creates śāstra. Brahmā and Vyāsa simply give specific form to what Viṣṇu creates.
What are the Writings of the Goswāmīs, Etc?
In the 1 in 1000 times that Krishna appears in Dvāpara, he soon thereafter realizes that he didn’t accomplish the objective of his descent (to spread Vraja-prema), so in Kali-Yuga he then becomes a premī-bhakta and again appears (as Śrī Kṛṣṇa Caitanya). He appears with his confidential assocaites.
He and those associates provide the inspiration that makes full use of Vyāsa’s Śrī Bhāgavata and allows Krishna prema to spread relatively widely throughout the world.
The writings of the Goswāmīs are direct expositions of the content of Śrī Bhāgavatam. This is a literal statement, and as you study the Bhāgavata deeply and the Goswāmī books literally, this fact stands clearly right in front of your nose.
What about “Sādhu” and “Guru”
These people explain and exemplify the Śrī Bhāgavata and other Śāstra. If they write or say things that are not completely supported by the conclusions of Śrī Bhāgavata, then their teachings and their followers are not counted among “Vedic” schools of thought. Buddhists are an example.
Sādhu and Guru have no independent authority apart from the śāstra. All philosophical authority is in the Śrī Bhāgavata and not elsewhere.
The members of a particular school or line will of course take full avail of the explanations of Śrī Bhāgavata given by their founders and ācāryas. Thus we approach the Śrī Bhāgavata through the Six Goswāmīs and their faithful followers. “Faithful” means “with fidelity.” One who comes to conclusions other than the conclusions arrived at by Śrī Jīva, Śrī Rūpa, etc. is not “faithful” – other credentials having no bearing to counterweight this judgement.
Thus no “new śāstras” are ever made, but something like that appears to happen in the attempt to explain the fundamental śāstra to new points of view. In time this inevitably causes the śāstra to lose coherence and integrity, which is why there is a scheduled necessity for Vyāsa.
The works of the six goswamīs, are not śāstra, but they are elaborations and explanations of Śrī Bhāgavata, by the followers of Śrī Caitanya.