Generally Dvaita students face, in the initial days, two questions about the necessity to acquire knowledge:
Strong Ignorance vs. Weak Knowledge: The Ignorance that covers the individual soul (jīva) is beginningless. Though it is not innate, it is very powerfully entrenched with our very selves. On the other hand, correct knowledge, even when produced, is nascent and hence weak. How can it overcome its much more formidable opponent i.e. beginningless ignorance? It is like trying to clean a golden object, which has collected many layers of dust over many years. Can occasional gentle brushing remove that dust or the impurities that have now settled in the object itself? Similar is our attempts to acquire correct knowledge. Is there any point at all?
The same question can be extended to our efforts. Our efforts are small and intermittent. The obstacles - a consequence of our karma in previous lives - are much stronger. They either block our efforts to acquire knowledge or pull us in the other direction. So is there any point in our efforts to break away from such obstacles?
In Dvaita Vedanta, knowledge related to an individual soul is of two types:
Svarūpa-jñāna i.e. its inherent knowledge. This knowledge is part of the soul's essential nature. This innate knowledge, like other innate aspects such as bliss is fixed; does not change. For muktiyogyas, this knowledge is pure i.e. always correct. However, this ‘inherently correct’ nature is experienced, almost completely, in Moksha only.
Except for some parts (like knowledge of oneself as the experiencer), other elements of this svarūpa-jñāna (like inherent knowledge about one's own dependence on the Infinite Lord, knowledge about Paramatma) are not manifested during samsAra. In Moksha, it is completely (almost) manifested.
Mano-vṛtti-jñāna i.e. refers to the knowledge acquired during samsAra. This acquired knowledge does not go into the jīva. (Such an admission - which is tantamount to essential changes in the jīva is scripturally and logically unacceptable). Instead all knowledge acquired through different pramāṇas including scriptures, goes into manas, i.e. it makes dents / modifications in the material manas. This is called mano-vṛtti or antahkaraNa-vṛtti (quite different from the same term in Advaita). This manas is a part of the prakritic layers covering the soul - one of which is again beginningless (linga-deha). At liberation, all prakritic layers, including this manas, wither off and the jīva’s innate knowledge, bliss etc. will shine through.
If all acquired knowledge is anyway going to be discarded / fall off, what then is the point in acquiring it in the first place?
Both these questions are addressed in Shrimad Anandatirtha Bhagavatpadacharya's Anuvyakhyana and Shri Jayatirtha muni’s Nyayasudha.
The context is about the inclusion of 'samaya-pāda' (2nd pāda) in the avirodha-adhyāya (2nd adhyāya). The entire 2nd adhyāya aims to dispel objections, from various sources, to the Vedanta doctrine. Of the 4 pādas within the 2nd adhyāya, the 2nd pāda focuses on critiquing other schools of thought, in terms of showing the irrationality of certain conclusions in those schools.
The question is about the relevance or the necessity of a critique of other schools of thought. Even if it is necessary in general, why should it be included in Brahmasutras and, particularly in the 2nd adhyāya?
(Shankara and Ramanuja have justified this inclusion in their commentaries. Their justifications are critically reviewed and dismissed by Sri Jayatirtha in Nyayasudha).
At the outset, Acharya justifies why it is impossible to completely eliminate such false doctrines (That justification is not translated here). Because of that, these false doctrines are eternal. They lapse into oblivion and resurface when a powerful proponent and other supplementary factors come together but are never completely decimated. So the purpose of this pāda is not complete elimination of these doctrines.
What then is the purpose?
The answer is thus: some genuine seekers, influenced by other doctrines, may have ignorance or have developed doubts or wrong knowledge. To remove such ignorance or wrong knowledge etc. in such people - is the purpose of this samaya-pāda.
(Ignorance and Wrong Knowledge even in genuine seekers are a given. Unless they are removed, just the right knowledge will not produce the necessary unwavering conviction in Vedanta. And this ignorance caused by flawed schools of thought can be removed only by powerful refutations. Thus the inclusion of samaya-pāda in 2nd adhyāya and in Brahmasutras is justified).
But then, isn't this also illogical? That the ignorance, which has been there since time immemorial, which is firmly situated and powerfully entwined with the impressions or the functioning of one's mind, will be removed or corrected by just-born correct knowledge (तत्त्वज्ञान) - does not make sense. Even if it does, such an ignorance will rise again from its own residues in the mind, and will definitely function in its own way (to produce doubts or cast questions regarding validity of Vedanta or accept illogical doctrines).
Acharya answers : तथाऽपि शुद्धबुद्धीनां ईशानुग्रहयोगिनाम् | सुयुक्तयः तमो हन्युः आगमानुगताः सदा |
The excellent logical arguments, based on scriptures, are given in this pāda to remove the darkness of ignorance and doubts present in people of pure minds i.e those whose intrinsic nature is to grasp correct knowledge, and who are eligible to receive Ishvara's grace.
Shri Jayatirtha explains the answer and its relevance to the previous question:
Some sentient beings are muktiyogya (eligible for moksha), some aren't. This pāda is not meant for removing the ignorance in the second category (i.e. mukti-ayogyas). On the other hand, it is meant to remove ignorance in the mukti-yogya folks only.
He continues:
ते च विशुद्धविज्ञानस्वभावाः ।
The eligible people's inherent nature is that of pure (i.e. yathartha = correct) knowledge. (That is, they are innately capable of grasping correct knowledge).
तथा च प्रमाणैः इदानीमेवोत्पन्नमपीदं मनोवृत्तिरूपं तत्त्वज्ञानं अन्तरङ्गभूतेन विशुद्धस्वरूपज्ञानेनोपोद्बलितं सत् बहिरङ्गमनाद्यपि सवासनं अज्ञानं समूलघातं हन्ति ।
Whatever knowledge is produced in the mind, through the functioning of (these logical arguments based on) these pramāṇas, will be strengthened greatly by such pure soul's innate knowledge. And such strengthened knowledge will be able to destroy, together with roots, even the beginning-less but still extraneous ignorance and all its products.
(Ignorance, though attached to the jīva from beginningless time, is not innate to the jīva. It can be removed. Mano-vṛtti cannot remove it unless it is aided by the jīva-svabhāva. That is, only if mano-vṛtti and svabhāva are aligned, the desired outcome i.e. elimination of ignorance is possible).
He further justifies:
स्वभावस्य सर्वतोऽपि बलवत्त्वात् । न चैवं प्रमाणवैयर्थ्यम् । स्वभावस्य बाह्यप्रयत्नसचिवस्यैव कार्यकारित्वात् । यथोक्तम् ‘विना यत्नं न हठो नापि कर्मे’ति ।
Indeed, jīva-svabhāva is stronger than ignorance (which is why liberation in future is a possibility). But why then does it not remove the ignorance on its own? Why (this mano-vṛtti from) these logical arguments or pramāṇas to remove ignorance? The answer is svarūpa(jñāna) produces the desired effect (of removing ignorance) only if it is aided by external efforts. This has been told (in Mahabharata-Tatparya-Nirnaya): Without prayatna, just the svabhāva nor the previous karmas fructify).
He continues:
किञ्च सर्वतोऽपि बलीयानीश्वरानुग्रह इति तावत्सुप्रसिद्धम् । अस्ति चासौ मोक्षयोग्येषु (जीवेषु) अनादित इति वक्ष्यते । तथा च तत्सचिवमिदं वृत्तिज्ञानं अज्ञानं अतिनिरूढनिबिडवासनानुबद्धं अनाद्यपि समूलकाषं कषत्येव अतो न व्यर्थेयं समयानां निराक्रिया इति भावेनोक्तम् ईशानुग्रहयोगिनामिति ।
Further, it is quite well known that the strongest factor is Ishvara’s grace. And such is present on Mukti-yogya jīvas and from beginningless time. Thus this mano-vṛtti-jñāna, though inherently weaker to beginningless and deep-rooted ignorance, uproots it, when aided by Ishvara’s grace. Thus, the refutation of these false doctrines is not futile.
That is: a study of these refutations produces mano-vṛtti-jñāna, that is aligned to the svarūpa-jñāna of a muktiyogya jīvas. Strengthened by such alignment with svarūpa-jñāna and even further by Ishvara’s grace, mano-vṛtti-jñāna removes ignorance. Thus these refutations have a purpose.
There is still one gap! Shri Jayatirtha closes that:
न चैवं तत एवाविद्यानिवृत्तिर्भविष्यति किं तत्त्वज्ञानेनेति वाच्यम् । ईश्वरानुग्रहस्य पुरुषप्रयत्नानुसारेणैव फलजननस्वाभाव्यात् । तथा चोक्तम् ‘फलप्रदो वासुदेवः अखिलस्ये’ति । अखिलस्य योग्यताकर्मप्रयत्नसाकल्यस्य न पुनरेकैकस्येत्यर्थः ।
If Ishvara’s grace is the strongest factor in destroying ignorance, let’s just admit that alone as the sufficient factor. Why consider these efforts to obtain correct knowledge as a factor? The answer is that Ishvara’s grace fructifies only in accordance and in alignment to our efforts. (That makes Him impartial and just). That is told in the line (now available in Garuda Purana) ‘फलप्रदो वासुदेवः अखिलस्य’: Vasudeva gives fruits based on everything (where everything = innate yogyata, karma and prayatna i.e. efforts) not just on one of those 3 factors.
It is noteworthy that Shri Jayatirtha has covered an important part in Mahabharata Tatparya Nirnaya, in the course of commenting on Anuvyakhyana. Acharya mentions the 3 factors in decreasing order of strength / importance in MBTN:
svarūpa (also called haTha, yogyatā) > past karma > prayatna (effort / endeavour).
All three are in Ishvara’s control. Though Prayatna is the weakest, it alone activates svarūpa and karma. So it does not matter if one has a lot of puNya. Only through some matching effort, does that merit manifest. Similarly, even if a jīva is muktiyogya, only through some matching effort, that eligibility for liberation actually fructifies.
This answers both questions about the necessity to acquire knowledge: Acquired Knowledge may be nascent but when aligned to Innate Knowledge and strengthened by Ishvara’s grace, it is capable of destroying beginningless ignorance, together with its roots. It derives its strength primarily from Ishvara’s grace. The same thing can be said about our efforts to get over bad past karma. Secondly, acquired knowledge may wither off at liberation. But it still has a purpose - to destroy ignorance.
May Shri Jayatirtha, his indwelling master Shrimad Anandatirtha and his indwelling master, Shri Vedavyasa, the Lord of all vidyā be pleased.
श्री मध्वेशकृष्णार्पणमस्तु