Sforno on Exodus 24:7/ספורנו על שמות כ״ד:ז׳

1ספר הברית. The book in which G’d’s words had been recorded as well as the laws concerning which the covenant was concluded. Reference has to be made to this book in verse four of our chapter.

2ויקרא באזני העם, Moses read out the contents so that the people would know what they had committed themselves to. Only by knowing the contents would they be prevented from violating the commandments inadvertently.

3נעשה ונשמע, a reference to action designed to ensure that they could obey G’d’s directives without thought of any reward that might be in store for them by doing this. We find a similar construction in Psalms 103,20 עושי דברו לשמוע בקולו, “who do His bidding, ever obedient to His bidding.”