It's how long David ruled from Jerusalem. Source: 1 Chronicles 3:4.

That's the book I'm reading currently. In the past it has seemed entirely boring. But recently I learnt that the Babylonian Chronicles are seen as reliable because of their matter of fact style and neutrality. The authors were simply concerned with documenting facts it seems. I asked myself if I read anything implausible in 1-2 Chronicles since it skips over the supernatural parts of Jewish lore. So I'm rereading it with that in mind and I'm discovering things now that I'm reading it closely. One is the above fact.

In historiography, a singular source is seen as unreliable, they look for multiple attestations. It's interesting how the genre of chronicles could be an exception to this rule although I don't know if it's a rule exactly or that the Babylonian one is an exception.

Masonic symbology is based on the Temple of Solomon so the adjacency of this fact shouldn't easily be dismissed as a coincidence. I believe that 33 is in part a reference to this. It's also how long Jesus lived according to popular belief so it wouldnt be the only Biblical 33. If they're obsessed with the Bible it's only natural we're going tfind 33s in that book.

This is less significant, but David's successor Solomon was far from the oldest son. He was more like in the middle. The youngest if you exclude the sons from extra women and so it's reminiscent of how Genesis defies expectations by making the youngest son the most prominent instead of the firstborn. But the duration of David's rule could have something to do with it. It could be older sons died off or he wanted one that would survive longer for fewer successions. I don't know how they selected successors.