Example Sentences:

Ramayana:  Sacrifice is the keystone of the teachings demonstrated by Rama and indeed by most of the heroic characters in the Ramayana.

Mahabharata:  Although many warriors considered Arjuna the keystone of the Pandava army, Duryodhana was especially concerned about Bhima, for he had vowed to kill Duryodhana and all his brothers. 

Bhagavad-gita:   Dharma is the Gita’s keystone — it underlies all the diverse themes covered in this philosophical classic.