Albert Barnes on Luke 4:17

There was delivered unto him. By the minister of the synagogue, or the keeper of the sacred books. They were kept in an ark or chest, not far from the pulpit, and the minister gave them to whomsoever he chose, to read them publicly.

The book. The volume contained the prophecy of Isaiah. It would seem, from this, that the books were kept separate, and not united into one as with us.

When he had opened the book. Literally, when he had unrolled the book. Books, among the ancients, were written on parchments or vellum that is, skins of beasts, and were rolled together on two rollers, beginning at each end, so that while reading they rolled off from one to the other. Different forms of books were indeed used, but this was the most common. When used the reader unrolled the MS as far as the place which he wished to find, and kept before him just so much as he would read. When the roller was done with, it was carefully deposited in a case.

The place where it was written. Isa 61:1,2