During medieval period, philosophers such as Ramanujacharya, Madhvacharya, Nimbarkacharya, and Vallabhacharya started Various Vaishnava Sampryadaya. Vaishnava-inspired scholars authored 14 Vishnu avatar-focussed Upanishads that are called the Vaishnava Upanishads. These Upanishads quote the texts included in the Brihadaranyaka Upanishad, Chandogya Upanishad, Katha Upanishad, Isha Upanishad, Mundaka Upanishad, Taittiriya Upanishad and others.
The Bhagavad Gita is a central text in Vaishnavism, and especially in the context of Krishna. The two Indian epics, the Mahabharata and the Ramayana also present Vaishnava philosophy and culture.
These philosophers established different schools of vedant which are as under:
SN Philosopher Vedant School Paramatma Jivatma (Chit) Maya (Jagat)
1 Shankar Acharya Advait Real, Nirgun Same as Paramatma Illusion
2 Ramanuj Acharya Vishishtadvait Real, Sagun Real Real
(1017-1137 AD) (Vishnu or Krishna) (Both are controlled by Parmatma)
3.Nimbark Acharya Dvaita-advait Real Real, exist Real, exist
(1028-1125 AD) (Krishna & Radha) (Both are dependent on Parmatma)
4.Madhv Acharya Dvaita Real Real Real
(1294-1317 AD) (Lakshmi Narayan) (Both are fundamentally different from Ishwar)
5.Vallabh Acharya Shuddha Dvait Real Real Real
(1479-1532 AD) (Krishna) (Different from Ishwar & Clouded by avidya) Power of Ishwar
Adi Shankaraacharya, Sri Ramanujacharaya, Sri Nimbarkacharaya and Sri Madhvacharaya were conferred title of Jagat guru.
Adi Shankara who believed to be advocated Jnana marg, also emphasised the importance of devotion and wrote Bhaja Govindam of 33 verses:
When intelligence (jnana) matures and lodges securely in the heart, it becomes wisdom (vignyana).
When that wisdom (vignyana) is integrated with life and issues out in action, it becomes devotion (bhakti).
Knowledge (jnana) which has become mature is spoken of as devotion (bhakti).