וַאֲנִ֗י זֹ֣את בְּרִיתִ֤י אוֹתָם֙ אָמַ֣ר יְהוָ֔ה רוּחִי֙ אֲשֶׁ֣ר עָלֶ֔יךָ וּדְבָרַ֖י אֲשֶׁר־שַׂ֣מְתִּי בְּפִ֑יךָ לֹֽא־יָמ֡וּשׁוּ מִפִּיךָ֩ וּמִפִּ֨י זַרְעֲךָ֜ וּמִפִּ֨י זֶ֤רַע זַרְעֲךָ֙ אָמַ֣ר יְהוָ֔ה מֵעַתָּ֖ה וְעַד־עוֹלָֽם׃ (ס)
And as for Me, this is My covenant with them, saith the LORD; My spirit that is upon thee, and My words which I have put in thy mouth, shall not depart out of thy mouth, nor out of the mouth of thy seed, nor out of the mouth of thy seed’s seed, saith the LORD, from henceforth and for ever.
Zohar
We have learned.... that the Torah that we need to learn on this night [Leyl Shavuot] is the Oral Torah, so that they may be purified together from the wellspring of the deep stream. Afterward, on this day [of Shavuot] Written Torah will come join her and they will be as one, as one couple above. Then it is proclaimed about him (Isaiah 59:21) 'And this is for Me My covenant with them said YHVH: My spirit that is upon you and My words I have put in your mouth (will not depart from your mouth, nor from your children's mouths...now and forever)'.