Chasidut zu Dewarim 27:12

Another way of explaining the word ‎היום‎ in our verse is that ‎although the “blessings” and “curses” which will in due course, be ‎pronounced inside the Holy Land at Mount Gerizim and Mount ‎Eyvol, (Deuteronomy 27,12-26) the “blessing of which Moses ‎speaks here applies immediately, and the people do not have to ‎wait until they have conquered part or all of the land of Canaan. ‎Moses spells out the blessing with the words: ‎אשר תשמעו‎, in order ‎for us to understand that the very fact that we hearken to G’d’s ‎instructions brings blessings in its wake. Merely listening to how ‎to perform a commandment is by itself the performance of a ‎commandment.‎‎