Reminding the Children of Israel that They were preferred above the Other Nations

Allah reminds the Children of Israel of the favors that He granted their fathers and grandfathers, how He showed preference to them by sending them Messengers from among them and revealing Books to them, more so than any of the other previous nations. Similarly, Allah said,

وَلَقَدِ اخْتَرْنَـهُمْ عَلَى عِلْمٍ عَلَى الْعَـلَمِينَ

Verse 47 asks the Israelites to call to their minds the blessing of Allah, so that the recognition of the benefits they have received may induce them to be thankful to Allah and thus to obey Him. The verse is addressed to the Jews contemporaneous with the Holy Prophet ﷺ while the blessing had been received by their forefathers. The point is that when a man receives a special favour, his children and grand children too usually partake of the benefits flowing from it; in this sense, the Jews who are being addressed may be said to have received the blessing themselves.

As for Allah giving preference to the Israelites "over the worlds", the phrase means that they were given preference only in certain matters, or only over a large part of men - for example, over the contemporaries of the earlier Israelites.