The next verse is helpful here:
Write in a book all the words that I have spoken to you. 3 For the days are surely coming, says the Lord, when I will restore the fortunes of my people, Israel and Judah, says the Lord, and I will bring them back to the land that I gave to their ancestors, and they shall take possession of it
...
31 The days are surely coming, says the Lord, when I will make a new covenant with the house of Israel and the house of Judah. 32 It will not be like the covenant that I made with their ancestors when I took them by the hand to bring them out of the land of Egypt—a covenant that they broke, though I was their husband, says the Lord. 33 But this is the covenant that I will make with the house of Israel after those days, says the Lord: I will put my law within them, and I will write it on their hearts, and I will be their God, and they shall be my people. 34 No longer shall they teach one another or say to each other, “Know the Lord,” for they shall all know me, from the least of them to the greatest, says the Lord, for I will forgive their iniquity and remember their sin no more
The book is for the people of the Old Covenant to know that a New Covenant is coming when they won't need a book anymore (which isn't to say that the Bible serves no purpose just that it isn't a precondition or requirement to know God although it can certainly be helpful). In a way it's a return to how things were eg. Abram didn't get to know God through a book.