When Battle for Azeroth was first talked about, and
In Rise of Azshara, a new system is tied directly to your amulet, the Heart of Azeroth. Players will, through play, acquire powerful Essences that can be put into the Heart of Azeroth, giving new abilities to players. Once you learn an Essence you add it to a collection and will be able to swap which Essence is active the same way you swap out Talents.
Each Essence has a major and minor power, with the minor powers tending to be passive effects, and the major being a flashy active effect. Only a few Essences have been revealed but they look like interesting tools, similar to getting a really good on use trinket.
The first Minor power unlock is when your necklace reaches level 55, with the second unlocking at 65. Essences that can be used by your class (ie you can play that role) will drop regardless of current spec.
Hopefully this makes the Azerite system more fun to use and different Essence choices will make for nice personalisation of your class, like an extra talent row.