I will arise and go now, for always night and day I hear lake water lapping with low sounds by the shore; (9-10)
Here we learn that the speaker is constantly reminded of the sounds of the place he feels is his home. He's homesick—for a home that doesn't yet exist.
While I stand on the roadway, or on the pavements grey, I hear it in the deep heart's core. (11-12)
No matter how far the speaker is from Innisfree, he feels drawn to it from deep inside himself. It's almost as if he's always there. So maybe he already is home—at least in his mind.