In plain words
When Dharmaja reached hell, everyone there was suffering its torments and crying out in anguish. The moment Dharmaja arrived in hell, all who were there felt a kind of gladness of mind. And the reason was nothing other than Dharmaja setting foot in hell! Meanwhile the prārabdha that Dharmaja had to undergo in hell came to an end. Now he had to go on to heaven. At that moment all the dwellers of hell begged Dharmaja to stay right there in hell. Then Dharmaja gave away the whole fruit of his merit to the dwellers of hell. As a result all their sins were destroyed, and they became fit to dwell in heaven. The dog, though, he would not leave behind. Even as he was going to heaven, Dharmaja said that if the dog that was following him were not let in, he too would not enter heaven. Then the dog took on its own true form, the form of Yamadharmarāja: ‘O Dharmaja! I took this shape because I wished to test you. Your devotion to Dharma will spread through the three worlds,’ it said. From that day Dharmaja's fame spread over the whole world.
It was by the sacrifice of the Pāṇḍavas that Bhārata won such great renown. In their 13 years of exile in the forest the Pāṇḍavas did not waste even a single moment. In that time they did tapas and gained great power and weapons. Arjuna was able to win the Gāṇḍīva. A small example. Arjuna was doing tapas, seated on top of a single pillar. Agni came and burned the pillar down. Even so, he did not waver in the least. Pleased with Arjuna's power of self-restraint, Agni became his servant. An apsaras came and said, ‘I want a son by you.’