This verse seems to seek to correct one of the many mistakes of the Israelites who rely so much upon their ancestors, and depend on their forefather's honour and sanctity! It says: ``That was a people that had passed away. They shall reap the fruit of what they did, and you of what you do! Of their merits there is no question in your case.''
Therefore, instead of boasting that you are the offsprings of such and such, try to purify your faith and heart, and correct your morals and deeds, because on the Day of Doom, no one will ask about what your progenitors did, rather each soul has to answer for its own deeds.