The source collar and the larva also serve similar purposes.
I personally believe it’s more that source=larva=Bhaal’s heritage
It ties our protagonist together, grants special powers, and possibly will be a driving our heroes and companions forward, through the story.
Keep in mind this is not a traditional tadpole that turns host into Mind flayer After couple days. From what I gather from interviews it’s more of Captain America tadpole which will put you under Mind flashers influence if you accept its powers.
