The Children of Israel scatter throughout the Land

Allah states that He divided the Jews into various nations, sects and groups,

وَقُلْنَا مِن بَعْدِهِ لِبَنِى إِسْرَءِيلَ اسْكُنُواْ الاٌّرْضَ فَإِذَا جَآءَ وَعْدُ الاٌّخِرَةِ جِئْنَا بِكُمْ لَفِيفًا

The preceding verse (169) contained a mention of a covenant made with the religious leaders of the Israelites in particular, that they shall not make any changes in the Torah and shall not ascribe to Allah anything but the truth. It has already been mentioned that they violated this pledge and distorted the contents of the Torah for petty amounts of money. This verse is an extension of the same theme. It says that there are some among their religious leaders who are truth-fully following the commands of the Torah and are firmly adhering to its guidance. They established the Salah as was required. The verse has provided with an assurance to such people that they shall not be deprived of their reward. That is, those who have been true to their faith and fulfilled its demands are righteous people among them.

There are some points of discussion related to this verse. The term 'Book' most probably refers to the Torah. Another possibility is that it refers to all the heavenly books of Allah like Torah, Injil and the Qur'an. Another point to be noted is that merely keeping the book of Allah and showing respect to it without following its' commandments does not fulfill the very object of its revelation. It is why the verse has used the word يُمَسِّكُونَ "Hold fast", in place of يَأْخُذُونَ or یَقرَؤنَ "those who take it or read it. Holding fast the Book requires to follow all it's injunctions and commands.