It's not really essential for BfA, no. "Before the Storm" is more or less a bottle-story - it primarily concerns itself with the event that reconnects the Forsaken with their Human family in Stormwind, and the disaster stemming from this incident. But it doesn't really connect to or inform BfA in any way that isn't covered by in-game quests, lore, or the comics that have been put out. "Before the Storm" enriches a few characters (Anduin, Baine, Genn, Turalyon, etc.) with additional influences, motivations, and events but none of that has a solid connection to BfA outside of secondary details.
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I'm not really sure on that score - the way the book is written seems to want to have it both ways, but more I think Anduin uses the pain of his old injuries as his own emotional litmus test, so to speak, a way of surveying his own feelings and then comparing them to what he thinks the Light wants or needs. The key here is that I don't think this "bone sense" is any kind of power - it doesn't grant him foresight (e.g. his trust in Calia proves disastrous regardless of what his senses tell him) and it doesn't plot a course that is ultimately beneficial to him.
I do think the Light is playing a part to further some agenda of its own, though; I get that from both Anduin being influenced by it as well as Saa'ra's cryptic words and shaping of Calia's trajectory. I think Anduin kind of relies on that sense as a crutch - it basically informs of him of what he already wants, and could also be a lever for the Light to use to subtly push him in a given direction as well.