1)
What is the comparison to the potter?
1.
Malbim (6, 10): I can do to you like the potter. Verses 9-10 discuss a decree to build a nation, and the nation sinned. Sinning is like the Kli breaking, and Hashem's retraction is like making a new Kli.
2)
Why did Hashem say "Ken Atem b'Yadi Beis Yisrael"?
1.
Radak (17:25): Hashgachah over people and ability is in Hashem's hand, and all the more so Yisrael, that His Hashgachah is always over them.