1)
Why does it specify the Goyim that remain around you?
1.
Radak: They saw the Churban, and soon they will see it built. They will know that this could be only from Hashem!
2)
How will they know that I built?
1.
Malbim: It is not natural; it is via Ru'ach ha'Kodesh. It is like creation ? everything was via His word. His word to the Nevi'im brought everything to action, miraculously.
3)
Why does it say "Dibarti v'Asisi"?
1.
Radak: I said this via the Navi, and I did like I spoke.
