Why does it say "va'Amartem"?
Radak: When I tell to you My Midah, you ask why the son did not bear the Father's sin, just like our fathers sinned, and are not here, and we bear their sins.
What do we learn from "veha'Ben Mishpat u'Tzedakah Asah"?
Radak: This explains why he should not bear his father's sin. However, you are Resha'im, therefore you bear also your fathers' sins ? "Poked Avon Avos Al Banim? l'Son'ai."
Malbim: This explains why he should not bear his father's sin. Physical traits and natures are inherited from fathers to sons, but matters of the Nefesh are not.
Why does it say "Shamar va'Ya'aseh Osam"?
Radak: He guarded Mitzvos Lo Sa'aseh, and did Mitzvos Aseh.
