What are stone tablets for in Noita?

There's an early game secret which I can pick up, and it is automatically placed in the hotbar. I can throw it, but I can't tell whether it has any effect at all other than being an object with gravity. Is it "just" lore, does it have an immediate effect, or is it something I can use later?

If I missed something in the UI that would be fine to point out. I would encourage keeping spoilers out, though.

You can drop the tablets on the altar located
_{(spoiler alert)}

to the right of the cave entrance, on a flying island right above the mountain.

This gives you a small amount of gold (150 IIRC), but also has a small chance of

summoning strong flying monsters.

Also, the tablets can be used as improvised projectiles.