Rashi on Exodus 23:20/רש"י על שמות כ״ג:כ׳

1הנה אנכי שלח מלאך BEHOLD, I SEND A MESSENGER [BEFORE THEE] — Here they were informed that they would once sin and that the Divine Majesty would have to tell them, (Exodus 33:3) “for ‘I’ will not go up among thee” (cf. Exodus Rabbah 32:3).

2אשר הכנתי means, WHICH I HAVE PREPARED in order to give unto you. This is the literal meaning of the verse. The Midrash (taking the word as connected in meaning with the term כִּוֵן “to put a thing in a line with” or “to make it correspond with” another thing) explains אל המקום אשר הכנתי to signify “to the place opposite to which I have long since established the seat of my Glory” (“the place” therefore denotes the Temple; cf. Rashi on Exodus 15:17). This is, according to the Midrash, one of the verses which implicitly state that the Temple in Heaven is situated exactly opposite (מְכֻוָּן) that on the earth (Midrash Tanchuma, Mishpatim 18)