1)
Why does it say "mi'Ketz Sheva Shanim"?
1.
Malbim: The Torah obligates freeing an Eved Ivri after he completes six years.
2)
Why does it say both "Lo Sham'u" and "v'Lo Hitu Es Aznam"?
1.
Malbim: They did not heed the Torah's Mitzvah, nor listen to Nevi'im who rebuked them about this.