As MistakeNot mentioned above, the Echo and Blessing of Light are two totally different things. The Echo is what grants immunity to Primal influence (tempering), not the Blessing, the later which is what Midgardsormr seals. The Blessing allows one to materialize the Crystals of Light and effectively have a direct line to Hydaelyn herself, allowing the Mothercrystal to directly step in and influence events (as in, protect her champion, the Warrior of Light).
What the Echo truly is, and where it comes from, is a major story revelation during ShB's story so I won't spoil it here for you.
Either way, both your questions are answered during Heavensward's storyline, so keep playing! It will all be revealed. Also, you're about to experience an earth-shaking event that was until Shadowbringers's final events my favourite part of the game. And still is. So keep at it, you'll get the answers you seek.!![]()