Tafsir of Al-Qasas 28:45

{ But We brought into existence generations }—meaning: We created generations between your time and the time of Moses—{ and the duration [of time] became long for them }—and the period extended, so the laws and rulings were altered, and the reports became obscured to them, especially to the last of them, who are those among whom you are. Thus, wisdom necessitated a new legislation and the recounting of the reports as they truly were. So, We revealed to you and recounted the reports to you.

The consequential element—namely, "We revealed"—is omitted, relying upon the mention of what necessitates it and indicates it: the bringing into existence of generations and the elongation of the time period. The essence of the meaning is: You were not present to know that, but you knew it through revelation. The reason for it is the extension of time until the laws were altered and the reports were obscured.

His saying—the Almighty—{ And you were not a dweller }—meaning: a resident—{ among the people of Madyan }—who are the people of Shu‘ayb, peace be upon him, and the believers. This is a negation of the possibility that the Prophet, may the Almighty bless him and grant him peace, had knowledge of some of what preceded in the story through hearing it from those who witnessed it.

And His saying—the Glorified—{ reciting Our verses to them }—meaning: reading to the people of Madyan by way of learning from them, just as a student reads a lesson to his teacher—{ the verses which state what took place between Moses, peace be upon him, and them, and what transpired between them and him. }

{ But We were messengers }—sending to you and revealing to you those verses and their likes. This rectification is like the previous one, except that there is no omission in it.