There was a Takanah instituted by Moshe Rabbeinu to read from the Torah on Monday & Thursday from that week's Parshah. See SA סימן קלה for more details on these halachos. On almost all weeks this leining is done until Sheini. (Except for the short Parshios at the end of Devorim where we lein past Sheini.) The one exception that I know of offhand is Parshas Vaeschanan. Why do we lein past Sheini during the week of Parshas Veaschanan? There are more than the 10 minimum required Pesukim needed to lein until Sheini, & Sheini does not appear to be in the middle of a topic, where one could say we should finish the topic before stopping?