Is it a sin to read parsha commentaries during leining?

Question

I understand that one is supposed to follow along with the communal Torah reading in Hebrew. But is this actually a requirement, as opposed to just a good thing to do? Another way of asking the same question: is it a sin to study the commentaries on the parshah during the reading instead of following along with each word?

I have the same question regarding the megillah on Purim. If I'm there at the megillah reading and studying the commentaries to the megillah while listening, have I fulfilled the mitzvah of listening to the megillah reading? In such a case, I would have been hearing the words as they were recited, even though I was concentrating on the commentary I was reading.

I'm not assuming the two question must have the same answer. I'm just asking these questions together because they're parallel questions.

Answer 1

The laws are brought in O Ch 146 (2) MB [8] and [14].
MB[8] allows one to learn quietly and to do “shnayim mikro v'echod targum” during the communal Torah reading as long as there are ten people who are paying attention to the reading.

So under those circumstances it is “just a good thing to do” to listen and certainly not a sin to “study the commentaries”. But the O Ch says that one has to listen to Parshas Zochor and Parshas Poroh.

The O Ch later says that the right thing for all parshiyos is to pay attention and listen. MB[14] says that one should not even do “shnayim mikro v'echod targum”.

So again it is “ just a good thing to do” to listen and certainly not a sin to “study the commentaries”.

Answer 2

A. torah reading torah reading is a mitzvah on the public--- there is no halakhic obligation to be present in the reading and thus no obligation to hear every word-- therefore even though its a mitzvah deoraysa--- its not a major issue to not be fully aware of the whole kria. and so it is up to you to you to decide whether you wish to read a commentary instead.

B. Meguillah reading--- While it is derabanan, it is a very "serious" mitzvah, one which the shulchan aruch claims that we stop learning torah in order to fulffil. The mitzvah is PERSONAL, ad so you are obligated to hear every single word, and if you missed one-- you have to read it all over again.