Q. Why do we say “Renew our days as of old” when we return the Torah to the ark? How can the past be brought back?
A. It would be nice to re-live the better parts of yesterday. It would be nice to re-encounter the opportunities we once had and, knowing what we now do, to make better use of them. But it isn’t going to happen. Yesterday has gone, and if we succeeded in bringing it back it would deny the next generation its right to grow up, develop, flex its muscles and make its own contribution. It would also come at a personal cost: we would have to put up with an age without modern sanitation or medicine (Kohelet 7:10 says: “Say not, ‘How is it that the former days were better than these?'”).
So you are right; we wonder what Jeremiah was thinking of when he spoke about the days of old (Echah 5:21). Yet in a spiritual sense there is something in it. At the time of Creation God made a pure, powerful light which was set aside for the righteous in time to come. That light contains all the answers. We may rightly yearn for the privilege of going back and earning its blessing.