Lu Xun says here:
夫 is probably the literary auxiliary for introducing a new topic.
有，I assume means “partly”
思理：I’m very unsure about this. Might go with 思辨能力: the ability for analytical thought 朗然:brightly, clearly?
My translation attempt:
As for the development of the populace, the merit in part depends on keeping the Ancient Tradition. But it’s keeping must happen with clear analytical thought, as a mirror or a clear lens, at times proceeding, at times looking back...
There are many parts about which I am uncertain. Can you point out mistakes or improvements?