[3:3] He has revealed to you the Book, by the truth
You did not know, O Muḥammad, what the Book was, nor the story of the lovers. But a matter of pre-eternal choosing came suddenly upon you, and cast you into an amazing affair, its proof sublime, its place of descent and occurrence precious.
[3:3 cont'd] confirming what was before it
i.e., verifying His promise to you in the books that came through the prophets (ʿa).
[3:3 cont'd-3:4] and He revealed the Torah and the Gospel * before as guidance to people, and He revealed the Criterion.
That is to say, 'Even though We revealed Our books to the messengers before you, We did not omit the remembrance (dhikr) of you from any book'. The one who spoke for them said:
With me from our absent beloveds
The remembrance of you
is their title page.
Just as We have extended the lights of the prophets through you, We have adorned all that We have revealed in remembrances with your remembrance.