To understand the Vedas, we need the help of the Itihasas and Puranas. There are eighteen Puranas, and these are classified as satvika, rajasa and tamasa Puranas, said M.A. Venkatakrishnan in a discourse. When satvik qualities were foremost in Brahma, he gave the sattvika Puranas. The sattvika Puranas are the ones which have been treated as important by Vaishnava Acharyas. And among these, the Vishnu Purana is considered the most important. It is called Purana Ratna. However, sometimes, Vaishnava Acharyas have also used statements in the rajasa and tamasa Puranas as references. Here they followed a rule. Wherever something that was said in a rajasic or tamasic Purana did not contradict what was said in the satvika Puranas, then they were acceptable. When they contradicted statements made in the satvika Puranas, they were rejected.
Vishnu Purana has a special quality. In other Puranas, a question is asked to Brahma about a specific devata. For instance, when a question is asked about Agni, Brahma extols Agni and the result is the Agni Purana. But in the case of the Vishnu Purana, the question asked by Sage Maitreya to Sage Parasara is not about any devata. It is a general question about the Supreme One, and Parasara replies that Lord Narayana is the Paramatma.
The Itihasas were written at the time the events described took place. The authors also are characters in the stories. Of the two Itihasas, Ramayana is superior. It may be argued that Mahabaharata is superior as it contains Bhagavad Gita and Vishnu Sahasranama. But the Gita and Vishnu Sahasranama together add up to a few hundred verses, and the total length of the Mahabharata is more than a lakh. In the Ramayana, however, Valmiki talks throughout about Rama.
