Is Learning the Religious Rules Obligatory?

Question: Will one be considered a sinner if he is careless in learning the religious rules that he frequently encounters?

Amswer: It is obligatory for a follower to learn the Masae'l which are of daily importance.[1] If his carelessness in learning religious rules leads to forsaking an obligation or committing a ḥarām action, he will be a sinner.[2]

1. Ayatollah Seyyed Ali Sistani , Islamic Laws Following a mujtahid (Taqlid)11.. 
2. Ayatollah Seyyed Ali Khamenei, Practical Laws of Islam, Rules of Taqlīd,  Caution, Ijtihād, and Taqlīd, Q3.