These four pesukim in Nitzavim (Devarim 30:11-14, source #1) present the commentators with two challenges:
1. What is "this mitzva" that the Torah refers to?
2. Why the need to reassure that "it" is not distant - in the Heavens or beyond the sea?

The commentators (and midrashim) take three different approaches about what "this mitzva" is:
a. The whole of Torah and Mitzvot;
b. Learning Torah;
c. Repenting - teshuva.

The vague, general expression, "this mitzva," certainly points in the direction of the first approach (a.), that it refers to the whole of Torah and Mitzvot. On the other hand, if that were the case, why limit it by saying, "this"? Furthermore, as the Ramban claims, it would have been more appropriate to use the commonly used more all-inclusive expression, "The whole mitzva that I command you today."

Others therefore see this section as referring to one particular mitzva. Many (including Rashi and the Midrash) explain that that mitzva is Talmud Torah, learning Torah, and bring evidence to support their case. The Torah is something to "get from the Heavens so that the people of Israel can hear it and do it." Plus, the immediately preceding verse (30:10) speaks of "listening to the voice of Hashem your G-d," and "this book of the Torah." The Ramban (along with Sforno and the Kli Yakar), is also motivated by the context of our section but comes up with a different conclusion.

The previous section in the Torah (Devarim 30:1-10) - as a whole, not just the last verse - deals with Teshuva, repentance. It has even been referred to as "Parshat Hateshuva". Its last verse ends with "when you return to Hashem your G-d with all of your heart and all of your being." Therefore, say the Ramban and others, "this mitzva" is repentance. They, of course, must assume that the Torah not only predicts repentance, but commands it.

The challenge now for the teshuva-approach is to explain why the people of Israel needs to be reassured that teshuva is not in the Heavens and not beyond the sea (#2 in our first paragraph above). In more detail: Israel is worried that repentance is hidden in the Heavens and distant beyond the sea and they need to be reassured that it is not. They are not commanded, G-d says to them, to go up to the Heavens or beyond the sea to get it. Rather, it is very close to them, in their mouths and hearts. What about repentance might be seen as hiding in the Heavens or distant beyond the sea?

The Sforno (possibly amplifying on the Ramban) assumes that the repentance spoken of (30:2) takes place even in exile (it is immediately followed by "Then Hashem your G-d will return your captivity" 30:3). The Heavens alludes to prophets and beyond the sea to distant wise men. The Jewish people must be told that they will not need a prophet to bring down any special message from Heaven indicating that repentance is possible. They also should know that repentance is a straightforward commandment. They will not need to ask any complicated halakhic questions of wise men beyond the sea. They already know what has to be done ("to do it") to repent - through internal change and regret ("in your heart") and verbal confession ("in your mouth").

The Kli Yakar sees this section as reassuring the sinner concerned about renewing his relationship with G-d. He notes how intense the repentance spoken of in the previous sections is - "You should return to Hashem your G-d" in the Hebrew is "ad Hashem Elokecha," implying that the penitent must reach G-d Himself. The baal teshuva, the penitent, is worried. Sin, we are told, causes the revealed Divine Presence to depart from this world. Sin causes the Shekhina to go up to the Heavens. Maybe, the sinner fears, G-d requires me to ascend to the Heavens to return to Him. Why should He descend to me when it was I who caused His Presence to depart? To this the sinner is reassured, "It is not hidden from you." You are able to return to the original closeness that existed between you and the Divine Presence - "ad Hashem Elokekha". You need not ascend to the Heavens. All you have to do is prepare your heart to return to Him and He will return to you and bring the Divine Presence down to you.

The Sforno and Kli Yakar develop why repentance might have been thought to require an ascent to Heaven or a trip to the other side of the sea. But what would taking repentance from Heaven and bringing it to the people to hear it and do it? "It is not in the Heaven, so that it should be said, 'Who will go up to Heaven and take it for us, so that we should hear it and do it?' It is not beyond the sea so that it should be said, 'Who will cross the sea and take it for us so that we should hear it and do it?'" This reads so smoothly if referring to the Torah, something that can be taken, then heard and done. How does this refer to Teshuva?

Perhaps "this mitzva" refers to teshuva, and our section's message about teshuva is that returning to Torah (= teshuva) is not as difficult as originally receiving the Torah. Israel has, over the generations, drifted away from the Torah they received at Sinai. Now, at the end of days, comes the time for a national repentance. Confronted with the enormity of the task Israel might think that it will only take place with special Divine intervention, a new Mount Sinai type experience. They might think that just as when the Jews originally got the Torah they had to have a Moshe ascend to Heaven to get it and they, as a nation, had to cross the Yam Suf (Red Sea) to get to Mount Sinai, so also in the end of days. They are therefore reassured that returning to the Torah does not demand ascending to Heaven or crossing the Sea. It is totally accessible, wherever and whenever. We always carry with us the ability to repent (even on a national level); it is within us, in our mouths and hearts.