Why had Duryodhana remained silent when Arjuna went to heaven (Swarga) for leaning DIVINE weapons?

 

Arjuna did not go to Heaven, as was narrated in the interpolated episodes in Vana Parva, ie., Arjuna’s fight with Shiva, Arjuna’s going to Heaven, etc. This can be evidenced from the following facts.

A) Arjuna learnt all types of Divine weapons from his Guru Drona, including Brimhashira. So, there was no necessity for Arjuna going to Heaven to learn from Indra and others.

 B) Pandavas lost everything in the First round of game of dice. And, getting humiliated, Dhritarashtra, with a view to appeasing humiliated Draupadi, gives back everything to Pandavas and asked them to proceed to their capital.

However, Duryodhana pressurises Dhritarashtra to call back Pandavas for 2nd round of game of dice. And, after their coming back, Shakuni says as follows:

अमुञ्चत्स्थविरो यद्वो धनं पूजितमेव तत् । महाधनं ग्लहं त्वेकं शृणु मे भरतर्षभ ॥

वयं द्वादश वर्षाणि युष्माभिर्द्यूतनिर्जिताः । प्रविशेम महारण्यं रौरवाजिनवाससः ॥

त्रयोदशं च सजने अज्ञाताः परिवत्सरम् । ज्ञाताश्च पुनरन्यानि वने वर्षाणि द्वादश ॥

अस्माभिर्वा जिता यूयं वने वर्षाणि द्वादश । वसध्वं कृष्णया सार्धमजिनैः प्रतिवासिताः ॥

त्रयोदशे च निर्वृत्ते पुनरेव यथोचितम् । स्वराज्यं प्रतिपत्तव्यमितरैरथ वेतरैः ॥

अनेन व्यवसायेन सहास्माभिर्युधिष्ठिर । अक्षानुप्त्वा पुनर्द्यूतमेहि दीव्यस्व भारत ॥

Shakuni then said, 'The old king has returned all your wealth. That’s good. But, O noble among the Bharatas, hear me—there’s a wager of immense worth. If you defeat us at dice, we will don deer skins and enter the great forest, living there for twelve years, spending the entire thirteenth year in an inhabited area, unrecognized. If we’re recognized, we must endure another twelve years of exile.

Conversely, if we win, you five Pandavas and Krishna (Draupadi) will wear deer skins and wander in the forest for twelve years, and again spend the thirteenth year unnoticed in a town. If recognized, a further twelve years of exile will follow. At the end of the thirteenth year, the kingdoms of each side will be returned by the other. O Yudhishthira, with this understanding, play with us, O Bharata, and cast the dice.'

So, if Duryodhana wins, all the Pandavas, alongwith Draupadi must spend 12 years in the Forest.

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If Arjuna went to Heaven and spend 5 years there, than spending on the Earth that too in the Forest, will Duryodhana remain silent?

No. He had been spying them and if Arjuna was not living in the Forest, Duryodhana would have demanded the Pandavas to spend another 12 years in the Forest.