Midrasch zu Schemot 29:42

2) The limitations: (Bamidbar 7:89): "And when Moses came to the ohel moed (for the L–rd) to speak to 1 him, that he heard the voice speaking to 2 him … and He spoke to him." (Shemoth 25:22): "And I will be appointed for you there, and I will speak to you … all that I will charge you with to the children of Israel." (Shemoth 29:42): "… where I shall appoint a time for you (plural) to speak to you (singular) there." (Shemoth 30:6):

7) — But let this exclude them only from appointment (i.e., meeting in the ohel moed), but not from dibroth! — It is, therefore, written (Shemoth 25:22): "and I will speak to you." — But let this exclude (from dibroth) only Israel, but not the elders! Let it exclude the elders, but not the sons of Aaron! — Let it exclude the sons of Aaron, but not Aaron himself! It is, therefore, written (Shemoth 29:42): "to speak to you" — With you there was dibbur, and not with any of the others.

8) And whence do we derive the same for the burnt-offering of (future) generations? From (Bamidbar 28:6): "a perpetual burnt-offering (like those) offered up (in the days of the investiture) at Mount Sinai." The burnt-offering of (future) generations (i.e., the tamid) is hereby likened to the burnt-offering of Mount Sinai. Just as the burnt-offering of Mount Sinai required a vessel, so the burnt-offering of the generations requires a vessel.