John Gill Commentary Ezekiel 43:21

"Thou shalt also take the bullock of the sin-offering, and it shall be burnt in the appointed place of the house, without the sanctuary." — Ezekiel 43:21 (ASV)

You shall take the bullock also of the sin offering Which was appointed for the sin offering, according to the divine direction, (Ezekiel 43:19), the prophet was to take it out of the herd, and separate it from the rest for this purpose, and deliver it into the hands of one of the priests: and he shall burn it in the appointed place of the house; that is, one of the sons of Zadok should receive it of the prophet, and burn it in its proper place; not within the house, without the court, but within the wall of the house:

this burning of it was typical of the dolorous sufferings of Christ; (See Gill on Ezekiel 40:39), or of the zeal and fervency of the ministers of the Gospel, in preaching a crucified Christ in the proper place, in the house and church of God: without the sanctuary; the holy place or temple, properly so called; or without the camp, typical of Christ's suffering without Jerusalem, and of his being preached not only there, but in the Gentile world; see (Hebrews 13:11Hebrews 13:12), this was the work of the first day of the consecration of the altar.