Wise words indeed. More from that source:
"Their zeal for knowledge may even prompt them to dig back into things that were published long before they came into the truth, expanding and deepening their understanding, and ever growing in Christian maturity. . . . Have you really studied these earlier publications? . . . If you are a newer one in the congregation, have you studied just one of the Society’s publications. . . . How can all these people get the things they have missed? Only by studying earlier publications and digging back through previous issues of The Watchtower kept in the library at your local Kingdom Hall. There is much in the way of spiritual riches and aids toward mature knowledge in these earlier publications, and their study is most certainly worth your time. By checking back through the Society’s earlier publications you will learn where to find the answers to questions that arise, and you will rejoice to see your understanding continue to grow.” (The Watchtower, May 15, 1957, pp. 311-317).
Nowadays, if you dare mention researching older material, you're cross examined for your "motives", reminded of the "New Light" doctrine, questioned where you obtained the earlier publications and then admonished to "keep up" with Jehovah's chariot, rather than catch up to it.