In addition to what Mjollnir and Noloe said, what we do know is that the planet Hydaelyn's "consciousness," for lack of a better word, was not always in its "true form." When Hydaelyn sensed that it was in danger, the Mothercrystal reformed and reached out to adventurers for help, bestowing upon them the Echo so that they would have an advantage against the coming threats.

This blessing from the source of life itself gives us certain unique benefits. We can see into the souls of those around us; understanding their words even if we do not speak their language, and even witnessing their past as if it were our own. Some clues say that this is thought by Eorzeans to be a simple instant replay of the past, but some clues hint that it may actually be that we temporarily become unstuck in time and are able to affect minor pieces of the past (possibly accumulating into something meaningful? Who knows.) Fan theories run both tracks, but we don't want to start writing fanon, now, do we?

One last benefit is that we're protected against the influences of certain enemies, such as the mind control of primals. We also seem to have some resistance to aetheric toxicity, but there aren't many practical examples of this or reasons we should care yet.

What this does give us, however, is the ability to investigate what is going on unhindered. We can talk to anyone in the world, witness anything they saw, and avoid nearly all deceit. We are meant to ferret out the threats to the Mothercrystal and take them down - but there always remains the chance that the reformation of the Mothercrystal was the goal of her enemy all along, as all crystals can be made to go dark...