What is the difference between "u'Shemartem" and "va'Asisem"?
Rashi: The former refers to Mishnah - learning; the latter, to carrying out what one learned.
What is "Hi" referring to?
Rashi: It is referring to the learning and the carrying out mentioned earlier in the Pasuk. 1
Targum Yonasan: It is referring to the Torah, which "u'Shemartem" "va'Asisem" themselves are referring to.
Rashi: And it is as if it says 'through the learning mentioned earlier, you will be considered wise men
What are the connotations of "Ki Hi Chochmaschem ... le'Einei ha'Amim"?
Rashi: It is through the study of Torah and its observance that we are considered wise and understanding in the eyes of the nations.
Seforno: It is by means of the Torah that we are able to answer the Apikores with logical arguments. 1
Why is it important to be considered wise in the eyes of the nations?
Seforno: Because, as the Torah goes on to explain, Hashem is close to us inasmuch as He answers us when we call to Him, a clear proof that He chose us from all the nations, and it would be a Chilul Hashem if the nations would consider us stupid.