Rashi and Rashbam: It is referring to the B'rachos and K'lalos ¹ (the Mitzvah of B'rachah and of K'lalah - Rashbam) that will be given on Har Gerizim and Har Eival. ²

R. Bachye; Moshe is teaching us that man's behavior is not decreed in Heaven, but that we have been given freewill and choice to do good or bad ^{1 2} - and that he is therefore responsible for his actions one way or the other, in which case he will be rewarded if he does good and punished if he perpetrates bad.

Seforno: The Torah is instructing us not to behave moderately as most people do, bearing in mind that everything one does results either in a B'rachah or in a K'lalah. There is no middle path (in Mitzvos) - because B'rachah implies success that exceeds one's basic needs, and K'lalah, a lack of success to attain even one's basic needs. ³

Da'as Zekenim #1 and Rosh #1: The Torah is instructing us to 'Choose the One who said "Anochi Hashem Elokecha".

Da'as Zekenim #2 and Rosh #2: Moshe is telling the people to see how he chose good, and how he is theefore different - in that his face radiates!

Kol Eliyahu and Divrei Eliyahu: If you will ask, 'How can we overcome the Yeitzer ha'Ra, which forces us to sin?', the answer is "Re'ei Anochi" - 'Anochi Eh'yeh Imach' ⁴ , Hashem will be with us - to help us overcome the Yeitzer ha'Ra.

Targum Yonasan: Moshe is instructing the people to take note of the two paths that he is placing before them - that of B'rachah and that of K'lalah.

Ramban (on Pasuk 29): It implies that we have the option ¹ of choosing B'rachah or K'lalah. ²

Kol Eliyahu and Divrei Eliyahu: It implies that, in the event that you will say that the path I am placing before you to take is not a good path - "Lifneichem", I am not forcing you to follow it.

Lev Eliyahu (in Sh'mos p.81): "Lifneichem" implies that the choice between B'rachah and K'lalah - that are supernatural - is confined to Yisrael.

R. Bachye #1: Because Moshe was addresing both the congregation at large and each individual simultaneously.

R. Bachye #2: Because, on the one hand, although Moshe was speaking to the congregation at large, since B'rachah and K'lalah are rooted in Midas Chesed and Midas ha'Din respectively, which only a few individuals can fully compehend, he said "Re'ei" ¹ wih regard to the individuals who are able to; whereas on the other hand, he said "Anochi Nosein Lifneichem" because B'rachah and K'lalah serve to encourage the people to fulfill the Mitzvos and to frighten them into not sinning. ²

Ba'al ha'Turim #1: Because the Torah is instructing each individual to take note of the choice that Hashem is placing before Yisrael as a whole.

Ba'al ha'Turim #2 (citing Yesh Omrim): Moshe is instructing Yehoshua to issue Yisrael the blessings and the curses after they cross the Yarden.

Ba'al ha'Turim #3: Because all the B'rachos and K'lalos in Seifer Devarim ³ are said in the singular ⁴ (even though they apply to the whole of Yisrael).

Ba'al ha'Turim #4 (citing Eruvin, 54b): This hints at the order in which Moshe taught Torah to the people, first to Aharon, then to his sons and finally, to the masses.

Kol Eliyahu and Divrei Eliyahu: In case you will say [that you are willing to choose good] when there are Tzadikim in the world, but what if you will be the only one to choose the good path, the Torah writes "Re'ei" (singular) - 'See for yourself, and do not pay heed to what others do!'

Oznayim la'Torah #1: Chazal have said that a person should always consider himself half meritous and half guilty and the world too, as if it was half meritous and half guilty, and that, consequently, if he performs one Mitzvah.he weighs down the scales of Mitzvos, thereby saving himself and the wold. It transpires that the B'rachos and K'lalos of the whole of Yisrael are dependent upon each individual, and the switch from singular to plural is most appropriate.

Oznayim la'Torah #2: In keeping with the principle 'Kol Yisrael Areivim Zeh la'Zeh', the Totah is teaching us here that one should not only perform Mitzvos oneself, but encourage others to do so as well.

Rashbam: Because it refers to the Mitzvah of B'rachah and K'lalah.

Da'as Zekenim and Rosh: It implies that in this world there is B'rachah and K'lalah, but in the world to come, there is only B'rachah ¹ (because in the days of Mashi'ach, Hashem will remove the Yeitzer ha'Ra from the world - Hadar Zekenim) ² .

Kol Eliyahu and Divrei Eliyahu: If we will say that if we will now choose the good path, what will be with the sins that you commited previously, the Torah adds "Hayom", to teach us that a Bal Teshuvah is like a newborn baby, provided that he continues to go on the good path afterwards.

Oznayim la'Torah (citing R. Bachye): It refers to the day mentioned in Devarim 29:3:2:2. ³

Kol Eliyahu and Divrei Eliyahu: Had the Torah written a"Nasati", we would have thought that Bechirah only applies at the beginning, but once a person has chose the wrong path, he cannot retract. Therefore the Torah writes "Nosen" (present) to teach us that a person can choose good until the day he dies.