Among the physics fans, there's still a lot of confusion - sometimes deliberately propagated confusion - about the basic questions surrounding gauge unification.
So what is grand unification and what it can do for us?
Aside from gravity described by Einstein's general relativity, there are three non-gravitational forces: the electromagnetic interaction - unified in the 19th century; the weak nuclear force; and the strong nuclear force.
The last two interactions include the adjective "nuclear": that's why you need to look at the microscopic world and to use quantum mechanics to appreciate what they really mean. And that's the reason why Einstein never understood anything about them. He thought that the goal was to unify electromagnetism and gravity only; his attempts to construct a unified field theory had no chance to succeed because gravity is the last force that may join the other forces - but only a long time after one understands the unification of electromagnetism with the two nuclear forces.