וּשְׁמַרְתֶּם֙ אֶת־כָּל־הַמִּצְוָ֔ה אֲשֶׁ֛ר אָנֹכִ֥י מְצַוְּךָ֖ הַיּ֑וֹם לְמַ֣עַן תֶּחֶזְק֗וּ וּבָאתֶם֙ וִֽירִשְׁתֶּ֣ם אֶת־הָאָ֔רֶץ אֲשֶׁ֥ר אַתֶּ֛ם עֹבְרִ֥ים שָׁ֖מָּה לְרִשְׁתָּֽהּ׃
그러므로 너희는 내가 오늘날 너희에게 명하는 모든 명령을 지키라 그리하면 너희가 강성할 것이요 너희가 건너가서 얻을 땅에 들어가서 그것을 얻을 것이며
Ibn Ezra
you will occupy [Hebrew: viyrishtem] the resh is vocalized with a ḥiriq because the vav is vocalized with a ḥiriq [cf. comment on 4: 1].
Sforno
ושמרתם את כל המצות אשר אנכי מצוך היום, the commandment to erect the stones in the Jordan as well as the stones you will take with you from the Jordan on which you will inscribe the Torah for the benefit of future generations so that the memory that these events really happened will be preserved.
Or HaChaim
ושמרתם את כל המצוה..למען תחזקו "You shall keep all the commandment in order for you to be strong, etc." Moses advances this argument against the people who suggested a temporary neglect of Torah study, something which physically weakens those who pursue it with intensity. The argument was that they had to husband their physical strength in order for them to conquer the Canaanites. Compare Sanhedrin 26 describing Torah study as a physically debilitating experience based on the word תושיה in Isaiah 28,29. I have mentioned previously that whenever Moses uses the expression כל המצוה in the singular he refers to Torah study. The reason Moses used the expression ושמרתם here, an expression associated with the observance of negative commandments is that neglect of Torah study would be considered a violation equal to transgressing a negative commandment. Moses concludes our verse by saying: "in order that you will be strong" to tell you that far from weakening you, Torah study and מצוה-performance will strengthen you in the forthcoming war by G'd. This is also the meaning of Proverbs 8,14: אני בינה לי גבורה, "once I have acquired insight (through Torah study) courage and strength will be mine."