Is not studying one's lessons considered a sin, despite understanding and benefiting from religion, and is it sufficient to convey knowledge to others?

Seeking religious knowledge and attending its gatherings are among the best deeds. "Whomever Allah wishes good for, He grants him understanding in the religion." Furthermore, treading the path of knowledge facilitates the path to Paradise. Continue attending lessons of knowledge, even if the benefit seems limited, and convey the good you have learned, after verifying its authenticity and disseminating it. There is no sin upon you for what you forget due to lack of revision, but neglecting knowledge and forgetting it are among the greatest losses.

We advise you to be patient and exert effort in learning gradually. Choose easy books in Fiqh (Islamic jurisprudence) and the Prophet's biography (Sirah Nabawiyyah), read them at home and with friends, and accustom yourself to reading religious sciences. We also recommend good companionship that helps in seeking and revising knowledge, frequent supplication, and reading about the lives of the Ummah's scholars.