Earlier, it was the time of Lord Brahma’s dina pralaya. 4 Yugas (Satya, Treta, Dvapara, and Kaliyuga) constitute 1 Mahayuga. 71 such Mahayugas constitute one Manvantara. And 14 Manvantaras constitute 1 Kalpa. This is the daytime for Lord Brahma. After Brahma’s daytime completes, he prepares to go to sleep. So, at that time, a dissolution takes place, which is known as dina pralaya.
In this dissolution, the Bhuloka (where we are living currently), Bhuvarloka (Space), and Svarloka (which consists of Svarga, Varunaloka, Yamaloka, Kuberaloka) are dissolved under the cosmic water and undergo destruction. Above Svarloka, there are Maharloka, Janoloka, Tapoloka, and Satyaloka (where Lord Brahma lives). These lokas remain intact and are unaffected. Above Satyaloka is Vaikunthaloka, the abode of Lord Vishnu.
This dina pralaya is different from the Mahapralaya. As I said, 1 Kalpa is the daytime for Lord Brahma. Lord Brahma has a lifespan of 100 years. Currently, Lord Brahma is 51 years old. So, once His 100 years are over, the Mahapralaya takes place, wherein everyone, including Lord Brahma and Lord Shiva, attains Pralaya, and only Lord Narayana is there, in His baalaroopa resting on the vatapatra.
So, this Mahapralaya is different from the dina pralaya.
So, this was the time period of dina pralaya, when Lord Brahma was feeling sleepy, and He didn’t have control over the Vedas and the presiding deities of the Vedas, which are known as Veda Abhimaani devatas. So, utilizing this opportunity, a demon by the name of Hayagriva came to Satyaloka, stole the Vedas, and ran away. Lord Brahma prayed to Lord Vishnu to rescue the Vedas.
Listening to Brahma’s prayer, Lord Vishnu assumed the form of a golden fish with a horn on it and went into the deep dina pralaya waters, found Hayagriva, and killed him there itself. This avatara which Lord Vishnu took is known as Matsya Avatara. Matsya in Sanskrit means fish. After killing the demon Hayagriva, Lord Vishnu, in His Matsya Avatara, came back to Brahma and returned the Vedas to Him.
Another story of Matsya Avatara comes in the Bhagavata. At the beginning of the creation, there was a king by the name of Satyavrata. He was a kind-hearted king and was a devotee of Bhagavan. Once, he was offering arghya to Surya in a river. As he took the water in his hand, he found that there was a small fish in his hand.
That fish said, “O King! Please do not throw me in the water. Or else, the bigger fish would eat me up. It is your duty to take care of and protect the people who take refuge in you. O King! Protect me.” On hearing this, King Satyavrata agreed and took the fish to his palace and kept it in a small container filled with water.
The fish grew up so much that it no longer fit inside the container. The king shifted it to another container. The same thing happened there too. Like this, he changed the containers, but the fish grew again, and the containers weren’t big enough for it. Then finally the king put it in a pond. There too, it grew up and didn’t fit.
Then, the king put the fish in a river. But again, the same happened. Finally, the king put the fish in the ocean. But there too, it grew up, and it wasn’t fitting in the ocean. The King said, “O Great fish! You aren’t any ordinary fish, because no fish grows at such a fast rate. There is something special about you. I think you are some divine fish, which has come to purify me. O divine fish! I think you are the Supreme Lord Vishnu Himself.”
At this, the fish said, “Yes. I am Lord Vishnu only. I have taken this Matsya avatara (fish-incarnation) to inform you that within a few days, jala pralaya (water-dissolution) is gonna take place, and hence, the protection of the Vedas, the Saptarshis (the 7 divine sages), aushadhis (medicines), all sorts of seeds for plants, and other kinds of knowledge must be protected.”
Lord Matsya said, “And this work is to be done by you, O king Satyavrata. On the day of dina pralaya, you would be carrying all of these on a wooden boat. Everything at that time is gonna submerge in the water. During that time, you remember me. I would come there, and you would tie the ship to my horn. I would carry you safely through the dina pralaya water. Don’t worry, my child. Everything will be fine.”
Saying thus, Lord Matsya gave upadesha to King Satyavrata, and this Upadesha which Matsya-roopi Narayana gave to King Satyavrata is what came to be known as the Matsya Purana, one of the 18 Mahapuranas, compiled by Lord Vedavyasa. After giving the Upadesha, Lord Matsya-roopi Narayana disappeared.
On the day of dina pralaya, at dawn, King Satyavrata, along with the Saptarshis and everything, went in a wooden boat through the dina pralaya waters. King Satyavrata remembered Lord Vishnu, and Lord Vishnu appeared in His Matsya roopa. King Satyavrata tied the wooden boat to Lord Matsya’s horn, and then Lord Matsya-roopi Narayana made them cross the dina pralaya waters and made them reach their destination safely.
They all landed on the Himavan parvata and thanked Matsya-roopi Narayana for helping them so much. From this incident, Matsya-roopi Paramatma gives us an important message that we must remember and keep firm belief in Bhagavan. And if we do so, then Bhagavan makes us cross the ocean of samsara easily and safely.
And then, the new creation started. This King Satyvrata was born again as Vaivasvata Manu. There are a total of 14 Manvantaras. And in each Manvantara, there is a ruler named Manu. The current Manvantara, in which we are, is the Vaivasvata Manvantara. And in this Manvantara, the ruler is Vaivasvata Manu, who is the son of Vivasvaan, named Aditya or Surya.
So, the protection of the Vedas was necessary because the Vedas are apaurusheya, which means they are not authored by anyone, but have come from Paramatma only. Plus, it has mantras which provide special powers, upon correctly reciting it at the correct time, with prescribed rules and regulations and that too in a clean environment, and keeping oneself and their minds clean.
So, this cannot be given to any unrighteous person like that, because if he uses it and gains power, then he may use it for the destruction of the world too, which is opposite to Dharma. So, that's why the protection of the Vedas was important. So, this was the story of Lord Matsya-roopi Narayana, who is the protector of the Vedas and is the provider of pure knowledge to even devatas led by Lord Brahma.
प्रोष्ठीशविग्रहसुनिष्ठीवनोद्धृतविशिष्टाम्बुचारिजलधे
कोष्ठान्तराहितविचेष्टागमौघपरमेष्ठीडित त्त्वमव माम् ।
प्रेष्ठार्कसूनुमनुचेष्टार्थमात्मविदतीष्टो युगान्तसमये
स्थेष्ठात्मशृङ्गधृतकाष्ठाम्बुवाहन वराष्टापदप्रभतनॊ ॥ १ ॥
O Lord Matsya, who has assumed the form of a fish! O Lord, who, by Your powerful breath, churned and raised the waters of the cosmic ocean! O Supreme Being, praised by Lord Brahma, who has safeguarded the Vedic scriptures and their vast body of knowledge! Please protect me. O Lord, who are beloved of the knower of the Self, who acted for the protection of the son of the Sun, Manu, at the time of the cosmic dissolution! O Lord, who stood firm and carried the wooden boat upon Your horn through the waters of the deluge! O Lord of resplendent golden form, please protect me.
~श्रीमद्वादिराजतीर्थविरचिता दशावतारस्तुतिः [SriVaadiraja Swamiji, Dashavatarastuti Shloka 1]
Hope this helps!
Jay SriRam!
ShriMatsya Roopi Narayana Abhinna ShriKrishnarpanamastu!