Ramban on Deuteronomy 31:21:1

וְטַעַם כִּי יָדַעְתִּי אֶת יִצְרוֹ אֲשֶׁר הוּא עֹשֶׂה הַיּוֹם, כְּטַעַם כִּי עַתָּה יָדַעְתִּי כִּי יְרֵא אֱלֹהִים אַתָּה (בראשית כב יב), שֶׁהִיא הַיְּדִיעָה בְּפֹעַל, כִּי הַיְּדִיעָה בֶּעָתִיד יְדִיעָה בְּכֹחַ, וְאִם לֹא חָטְאוּ יִשְׂרָאֵל בַּמִּדְבָּר וְלֹא נוֹדַע יִצְרוֹ בְּפֹעַל לֹא הָיָה הָגוּן שֶׁיָּעִיד בָּהֶם שִׁירָה לֵאמֹר גָּלוּי לְפָנָיו שֶׁתֶּחֶטְאוּ וְאָעִידָה בָּכֶם שֶׁתִּמָּצֶאנָה אֶתְכֶם רָעוֹת רַבּוֹת וְצָרוֹת כָּזֶה וְכָזֶה, אֲבָל הָיָה הָרָאוּי שֶׁיִּתֵּן לָהֶם הַתּוֹרָה בִּידִיעָה סְתָם, אִם תֹּאבוּ וּשְׁמַעְתֶּם טוּב הָאָרֶץ תֹּאכֵלוּ וְאִם תְּמָאֲנוּ וּמְרִיתֶם חֶרֶב תְּאֻכְּלוּ, אֲבָל עַתָּה שֶׁנּוֹדַע גַּם לָהֶם יִצְרָם הָרַע וְלִבָּם הַזּוֹנֶה יַגִּיד לָהֶם כָּל הַקּוֹרוֹת אוֹתָם, כְּעִנְיָן שֶׁנֶּאֱמַר (ישעיה מח ד ה) מִדַּעְתִּי כִּי קָשֶׁה אָתָּה וְגִיד בַּרְזֶל עָרְפֶּךָ וּמִצְחֲךָ נְחוּשָׁה וָאַגִּיד לְךָ מֵאָז בְּטֶרֶם תָּבוֹא הִשְׁמַעְתִּיךָ: FOR I KNOW THEIR INCLINATION WHICH THEY HAVE SHOWN THIS DAY. The meaning thereof is like the expression, for now I know that thou art a G-d-fearing man,⁴⁰Genesis 22:12. which is knowledge become actualized, for knowledge of the future is knowledge in potential.⁴¹See Ramban ibid., (Vol. I, p. 279). Now, if Israel had not sinned in the wilderness and the recognition of his temperament had not been actualized, it would have been inappropriate for him to testify against them in the Song, saying that it is known to Him that you will sin and therefore I call [heaven and earth] to witness that many evils and troubles³³Verse 17. like such and such will come upon you. Instead it would have been proper that He give them the Torah with unspecified foreknowledge: If ye be willing and obedient, ye shall eat the good of the Land; but if ye refuse and rebel, ye shall be devoured with the sword.⁴²Isaiah 1:19-20. But now, that their bad temperament and their straying heart⁴³Ezekiel 6:9. had become known to them as well, He told them all that would occur to them. This is similar to what is said, Because I knew that thou art obstinate, and thy neck is an iron sinew etc., therefore I have declared to thee from of old; before it came to pass I announced it to thee.⁴⁴Isaiah 48:4-5.