פּירוש אויף דברים 27:9

הסכת — Understand this as the Targum does: אצית listen!

Moshe and the Levitical kohanim spoke just as it was related earlier [: 1] that he spoke along with “the elders of Israel”. But in all such cases the primary speaker was Moshe.

וידבר משה והכהנים הלוים, Moses co-opted the priests to caution them on the importance of studying the Torah in depth. This was because it was their primary duty to teach the Torah to the people. [service in the Temple occupied only a few days’ a year of each priest’s time. Ed.] (compare Deut. 33,10 יורו משפטיך ליעקב, “they shall teach Your laws to Yaakov.”)

היום הזה נהיית לעם THIS DAY YOU HAVE BECOME THE PEOPLE [OF THE LORD YOUR GOD] — On each day it should appear to you as though it were “today” that you have entered the covenant with him (Berachot 63b).