The visual modulation (VM), as it came to be known, served as a one-way conduit of information from the stars to us. Apparently there were quite a few chatterboxes sending us signals, and now that we were able to listen it was interesting what they had to say.
The reason stellar VM was used was that Fours, as sentient lifeforms in the galaxy called themselves, could be influenced by it as their brains evolve to consume photons in the visual spectrum. This influence isn't malicious, it just nudges people towards ideas and concepts that need discovery or sharing.
Apparently one of the things this does, as a group of Fours approach "disclosure" as the surprising fact that they're not alone in the universe is called, is cause media for that group to expand towards stories of aliens. For humans there was a great rich history of science-fiction, but apparently the author who got closest to what was really going on was Douglas Adams, and his Hitchhiker's Guide to the Galaxy (well part of it).