וְיָדַעְתָּ֣ הַיּ֗וֹם וַהֲשֵׁבֹתָ֮ אֶל־לְבָבֶךָ֒ כִּ֤י יְהוָה֙ ה֣וּא הָֽאֱלֹהִ֔ים בַּשָּׁמַ֣יִם מִמַּ֔עַל וְעַל־הָאָ֖רֶץ מִתָּ֑חַת אֵ֖ין עֽוֹד׃
know this day, and lay it to thy heart, that the LORD, He is God in heaven above and upon the earth beneath; there is none else.
Sforno on Deuteronomy
וידעת היום, it behooves you therefore to understand how these miracles confound any theological theories that are not in agreement with Jewish tradition.
Or HaChaim on Deuteronomy
וידעת היום, "and you should know this day, etc." What is it that the people should know about on this day rather than on any other day? What knowledge were they to store up in their hearts? Perhaps Moses referred to the need to subdue the evil urge which lurks within all of us. Moses may have referred to 10 such pieces of information which the Israelites were to store up in their hearts.