So now we can understand why Vyasji is the greatest acharya. And, in the Vachanamrut, Bhagwan Swaminarayan has declared him as the final authority, as far as the shastras are concerned.

He was born on an island in the holy river Yamuna, on Ashadh Purnima over 5,000 years ago. His father was Parashar rishi and mother, Satyavati.
He studied under his father, as well as other great rishis such as, Vasudev and Sanakadik. He then taught the Vedas to his pupils. He had four famous sons: King Pandu - father of the Pandavas, Dhrutarashtra - father of the Kauravs, Vidurji - famous for his text, Vidurniti, and Shukdevji - famous for his wisdom given to King Parikshit, in the Shrimad Bhagwat. The Bhagwat is the 18th Puran which Vyasji wrote. In it he has described Shri Krishn’a divine episodes. He then attained inner peace.

After thinking deeply about all the shastras that he wrote, he described the most important goal of life.
Alodya sarva shastrani, vicharya cha punaha punaha, Idamekam sunishpannam dhyeyo Narayano Harihi.

i.e. After repeatedly reflecing on all the shastras, I have drawn one conclusion, that life’s goal is to realize Bhagwan Narayan.

Vyasji and Bhagwan Swaminarayan.

Besides declaring Vyasji as authoritative, Bhagwan Swaminarayan has praised him in eleven Vachanamruts :
In the Shikshapatri (93-95), the code of conduct written by Bhagwan Swaminarayan, He lists eight shastras as authoritative:-
(1) Four Vedas
(2) Vedant Sutras (Brahma Sutras)
(3) Vasudev Mahatmya of the Skand Puran
(4) Shrimad Bhagwatam
(5) Vidurniti in the Mahabharat (Udyog Parva 33- 40)
(6) Vishnusahastranam in the Mahabharat
(7) Bhagvad Gita in the Mahabharat
(8) Yagnavalkya Smruti
Of these eight, the first seven are all by Vyasji !

In honor of Ved Vyas as the foremost acharya and guru in Sanatan Dharma, the Guru Purnima festival is celebrated annually on Ashadh Punam. This is also known as Vyas Purnima. On this day, the spiritual guru is offered pujan. In the BAPS sanstha, we do pujan of our guru, His Divine Holiness Pramukh Swami Maharaj.