Was the Bhagavad Gita an interpolated one in the Mahabharata?

It is an interpolated work, added at a later date to Mahabharata, in view of the following reasons.

I) Voluminous

Sage Vyasa composed the Jaya Samhita, the original version of Mahabharata, in 8,800 shlokas.

The present day available version of Mahabharata contains nearly 75,000+ shlokas. And, the Bhagavadgita alone contains 700 shlokas.

How could Sage Vyasa have included such a voluminous portion of Gita in his Jaya Samhita, where everything was told in a brief manner?

II) Message of Kunti (Udyoga Parva)

When his mission to arrange for reconciliation between Kaurvas and Pandavas failed, Shri Krishna intimates everything to Kunti. Then, Kunti sends the following message to Pandavas, and with specific reference to Bhima and Arjuna.

नमो धर्माय महते धर्मो धारयति प्रजाः ॥

एतद्धनञ्जयो वाच्यो नित्योद्युक्तो वृकोदरः । यदर्थं क्षत्रिया सूते तस्य कालोऽयमागतः ॥

न हि वैरं समासाद्य सीदन्ति पुरुषर्षभाः ॥

विदिता ते सदा बुद्धिर्भीमस्य न स शाम्यति । यावदन्तं न कुरुते शत्रूणां शत्रुकर्शनः ॥

स्त्रीधर्मिणी वरारोहा क्षत्रधर्मरता सदा । नाध्यगच्छत्तदा नाथं कृष्णा नाथवती सती ॥

तं वै ब्रूहि महाबाहो सर्वशस्त्रभृतां वरम् । अर्जुनं पुरुषव्याघ्रं द्रौपद्याः पदवीं चर ॥

विदितौ हि तवात्यन्तं क्रुद्धाविव यमान्तकौ । भीमार्जुनौ नयेतां हि देवानपि परां गतिम् ॥

तयोश्चैतदवज्ञानं यत्सा कृष्णा सभागता । दुःशासनश्च यद्भीमं कटुकान्यभ्यभाषत ॥

पश्यतां कुरुवीराणां तच्च संस्मारयेः पुनः ॥

'I honour righteousness, which is greater than all. It is righteousness that upholds all living beings. You must communicate this message to Dhananjaya. Then to Vrikodara, who is always eager to act, convey these words: 'The moment has arrived for what a Kshatriya woman brings forth a son for!

Those who are the best among men never lose heart in battles. You know how Bhima feels. That warrior against foes is never satisfied until he conquers them.

Alas, beautiful Krishna, ever devoted to Kshatriya ways, had no defender on that day, despite being married to such mighty protectors.'

O you of strong arms, tell that fierce warrior, Arjuna, the greatest of all fighters, that he should always follow the path shown by Draupadi. You know well, Kesava, that Bhima and Arjuna—those fearsome agents of destruction—can make even the gods submit to their power.

Is it not a disgrace that their wife, Krishna, was dragged into the assembly? O Kesava, remind them of all the cruel and harsh words that Dussasana hurled at Bhima in front of all the Kuru warriors.

——

Shri Krishna conveyed her message to Pandavas.

If anyone thinks that, after hearing that inspiring message from his mother, Arjuna becomes so weak-minded necessitating Shri Krishna to give such a lengthy spiritual lecture, it is just childish.

III) Arjuna’s message to Duryodhana through Uluka

Duryodhana sends Uluka, son of Shakuni, to convey his intimidating message to Pandavas. After Uluka conveys that message, Arjuna says as follows:

भावस्ते विदितोऽस्माभिर्दुर्बुद्धे कुलपांसन । न हनिष्यन्ति गङ्गेयं पाण्डवा घृणयेति च ॥

यस्य वीर्यं समाश्रित्य धार्तराष्ट्र विकत्थसे । हन्तास्मि प्रथमं भीष्मं मिषतां सर्वधन्विनाम् ॥

O wretch of thy race! Thou hast done it, believing that sons of Pandu will not, from kindness, slay the son of Ganga. Know, however, O Dhritarashtra's son, that I will slay that Bhishma first in the sight of all the bowmen, relying upon whose strength thou indulgest in such boasts!

——-

Thus, it can be understood that Arjuna was not weak-minded, based on his words spoken just before the great war took place.