Then he took the book of the covenant refers to the book in which the terms of this agreement between Yahweh and the people were written. Good News Translation adds the phrase “in which the LORD’s commands were written,” in order to make this clear, although these words are not in the Hebrew. And even with this addition, it is not clear who had written this, nor when it was written. The present context suggests that this is what Moses wrote in verse 4, the earliest written form of the laws in 20.22–23.33. In languages where all of this needs to be made explicit, one may say, for example, “Then he [Moses] took the Book of the Covenant in which he had written the LORD’s commands.”
Book of the covenant may also be rendered as “Book of God’s Agreement with his People.” (See the comment on covenant at 19.5.) The word for book is a general term for a written document, which in this case probably was either a papyrus scroll or a large piece of leather. In some languages it may be better to translate “Then Moses read aloud the LORD’s commandments that he had written down.” Contemporary English Version has a similar model: “Then he read aloud the LORD’s commands and promises.” What he read, the book of the covenant, probably refers to the mishpatim, which is better translated as “commandments.” (See the introductory comments before 20.22.)
And read it in the hearing of the people is literally “and he called [it] in the ears of the people.” Good News Translation puts it more naturally: “and read it aloud to the people.” And they said introduces the same formula, or ritual response, All that the LORD has spoken we will do. This is identical with 19.8 and similar to the one in verse 3. (See the comments there.) And we will be obedient, literally “and we will hear,” is an addition to the response in 19.8 and verse 3. It may be more natural to interchange we will do and we will be obedient, as several translations have done: “we will heed and do” (New American Bible), “we shall obey, and do” (Revised English Bible), and “we will obey the LORD and do” (Good News Translation).
Quoted with permission from Osborn, Noel D. and Hatton, Howard A. A Handbook on Exodus. (UBS Helps for Translators). New York: UBS, 1999. For this and other handbooks for translators see here .