He says that His pious and God-fearing servants believe in the unseen...
He says that His pious and God-fearing servants believe in the unseen, keep up prayer, spend out of the sustenance given to them by Allah, believe in that which was revealed to the Apostle and to the previous apostles and are sure of the life hereafter (vide verses 2-5 of this chapter). Allah guides them through the Qur'an; and then He shows the contrast between them and the infidels and hypocrites. Then the talk turns to the affairs of the people of the Book and especially the Jews.
It explains how Allah, in His grace, guided them, and exalted them with His bounties and favors. And what was their response to all those favors? They became arrogant, disobeyed the commandments of Allah, and repaid His bounties with ingratitude; they stood against Allah and His apostles, bore malice against His angels, and made differences between one apostle and the other, and one book and the other.
As a result, Allah laid on them heavy burdens, like the order to kill their own people; and imposed upon them that which they had no strength to bear, like turning them into apes, and sending lightening and plague from the sky on them. After going into all these details, Allah recounts in these two verses the good attributes of the Apostle and the believers who have followed him; He shows that their condition is /in clear contrast with that of the people of the Book.
They have responded to the divine bounties and guidance with submission and obedience; they believe in Allah, His angels, His books and His apostles, without making any difference between any of the apostles. And they know their own limitations as powerless mortals, and recognize the all-pervasive power of Allah. Although they have unconditionally submitted to the Caller towards the truth, they confess that they cannot do justice to that Call because of their inherent weakness and ignorance.
They are afraid that they may transgress the limit by forgetfulness or mistake, or that they may fall short in their duties of divine worship; they are worried lest a sinful act puts them in disgrace, as happened with the people of the Book before them.
Therefore, they beseech the All-merciful Lord and pray to Him not to punish them if they forget or make a mistake, not to lay on them a burden and not to impose upon them that which they have not the strength to bear; they entreat Him to pardon them, to forgive their mistakes and to have mercy on them, and to help them against the unbelieving people.