As per Shastra, is it necessary for a Brahmin to impart the spiritual knowledge which he has attained to others?
Does he incur any sin if he does not do so?
One popular reference is - ऋषि ऋण Rishi rina and देव ऋण deva rina
Spiritual knowledge is considered a debt from elders. It can only be repaid by teaching others, else debt remains unpaid.
How to learn from a master?
Refer Gita 4-34