Most of the experiential knowledge of ancient seers of India are captured in Vedanta (Upanishads).
The crux of concepts in Vedanta was explained by SreeKrishna in Bhagwat Gita, which were persisted in Mahabharatha by Maharshi Vyasa.
The core idea of Bhagwat Gita again is to understand the God, and this highest principle is extracted and persisted by the great sage Vyasa in Vishnu Sahasranama.
Chanting and meditating on Vishnu sahasranama is thus considered as the highest Dharma. In fact it’s so revered that when someone say’s just Sahasranama, it almost always refers to Vishnu sahasranama, even though there is a Sahasranama dedicated to almost every high soul in Sanatana Dharma.
This series will also have first stanza of Sahasranama to get you started.
Best wishes !