There was a thread on EN World a few months back about the role of sages in D&D. In AD&D, there was a fair amount of material in the DMG about the services offered by experts in various fields. If the characters needed to learn the history of the Forgotten City of Thar, they could plunk down some cash and hire the services of an expert.
Over the years, that sort of expertise has shifted from NPCs to characters. Non-weapon proficiencies, and later the skill system integrated into D&D, gave the characters the opportunity to become experts themselves. The sage as an important element of the game faded away.
On one hand, that makes things easier at the table. The DM can salt a dungeon or other location with strange runes, crumbling statues, and other bits that allow for skill checks as a way to add depth, background, and hints to the game.
On the other hand, sages provided a few nice benefits. They are a great way to give the party an interesting, non-combat challenge, a fun NPC to interact with, and a world that feels like a living, active place outside of the immediate bounds of an adventure. They set up a plausible situation where the PCs have to make an NPC happy in order to achieve their goals.
There's a rather easy way to combine the two approaches, giving the characters the benefits of skills like Arcana or History while making sages (and similar NPCs) useful, interesting resources. Simply put, most experts combine off the cuff knowledge with a thorough understanding of how to find an answer. That can easily extend to the PCs.
When the characters discover strange runes carved on to a seemingly impenetrable steel door, a skill check points the way to the expert that can tell them about the runes. The character's knowledge isn't absolute, but it does carry with it an understanding of the experts, important books, and other lore surrounding the topic.
Even better, you can frame that knowledge with an interesting choice. Perhaps the characters can recall two experts who might know about the runes. Yulgash the Exile's knowledge is unmatched, but he dwells in the Forest of Brambles ever since the townsfolk caught his servants pillaging the graveyard. Tharan the Radiant is a close second, but as a high priest of Pholtus any inquiries to him might generate unwanted entanglements. Giving the characters real options is an important part of D&D, and this is one more way to introduce that.
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