(9.40ab) (Hinayanist) “Since we can attain liberation by gaining a direct realization of the four noble truths,
What is the point of striving to realize emptiness, lack of true existence?”

Realizing the emptiness of the Prasangikas is hard. Further, our ignorance will come up with all sorts of excuses as to why we do not actually have to realize emptiness. For example, we are often very happy to read Dharma books about love, compassion, our precious human life and so forth. But the idea of picking up Ocean of Nectar and studying intricate debates about emptiness seems a daunting task to say the least. We get lost and we do not see the point, and just like we did with math while we were in school, we think we will never need this so why bother trying?

Here, the Hinayanists are doing the same thing. They are saying we merely seek to attain individual liberation, and Buddha explained we can do so through realizing the Four Noble Truths, so why should we bother listening to all you Prasangikas babble on about lack of true existence and the nonexistence of self-cognizers and so forth? 

What are the Four Noble Truths? The first is true suffering, which means recognizing that we are trapped within samsara. The second is true origins, which means understanding the root of our suffering in samsara, namely delusions. The third is true cessations, which refers to the cessation of true origins within our mind. And the fourth is true paths, which is the method for attaining true cessations.

(9.40cd) It is necessary because the scriptures explain that without the path of wisdom realizing this emptiness,
It is impossible to attain even the small enlightenment of self-liberation.

The Prasangika answer to this objection is the wisdom realizing the emptiness of inherent existence is implied within the Four Noble Truths.  For Prasangikas, the source of all delusions is the ignorance grasping at inherent existence. And true cessations are realizing that all of the things that we normally see do not exist at all. This is attained through true paths, which are meditations on the correct view of emptiness. Without realizing emptiness, it is not possible to eliminate all of our delusions, and therefore escape from samsara. Thus, even to attain individual liberation of a Hinayanist requires realizing emptiness.

The basis for this view comes from the Mahayana scriptures explaining emptiness.  

(9.41-4) (Hinayanist) “Because we do not believe in the Mahayana, your quoting from Mahayana scriptures is pointless.”

The Hinayanist objection to the Prasangikas saying emptiness is implicit within the Four Noble Truths is the basis for the Prasangika view is the Mahayana scriptures. But the Hinayanists reject the Mahayana scriptures as being actually taught by Buddha, so therefore they say quoting from them is pointless.

We both believe that the Hinayana scriptures are valid;
So you should apply your reasons for believing the Hinayana equally to the Mahayana.
Thus, we understand that both are the holy Dharma taught by Buddha himself.

First of all, in the real world we would never try to disagree with someone who follows another path. If their path works for them, then we are happy for them, even if they reject our own path. We do not need to convert anybody to the mahayana view, but we are happy to clarify points if someone is actually open minded. If they are not open minded then we just leave them to their path and that’s it.

In this context, we are assuming that the person we are speaking with is a Buddhist and is open minded about the possibility of mahayana scriptures, and so therefore we simply ask the questions to try overcome their doubts. But in the context of our own individual contemplation of Shantideva’s guide, we should recognize all the objections as doubts we may have within our own mind. Perhaps we ourselves doubt whether the mahayana or the vajrayana or the ganden oral lineage and so forth was actually taught by Buddha. This may cause is to doubt the authenticity of the instructions that we receive.

Shantideva’s answer to the Hinayana’s objection is they should apply whatever is the criteria they use for assessing the validity of the Hinayana scriptures to assessing whether the Mahayana scriptures are also valid. It is fair to say if the criteria is good enough for their scriptures then that same criteria should be good enough for evaluating other scriptures.