exodus 30:6 And thou shalt put it before the vail that is by the ark of the testimony, before the mercy seat that is over the testimony, where I will meet with thee. - Free Bible Online

      6. thou shalt put it before the veil that is by the ark of the testimony--which separated the holy from the most holy place. The altar was in the middle between the table of showbread and the candlestick next the holy of holies, at equal distances from the north and south walls; in other words, it occupied a spot on the outside of the great partition veil, but directly in front of the mercy seat, which was within that sacred enclosure; so that although the priest who ministered at this altar could not behold the mercy seat, he was to look towards it, and present his incense in that direction. This was a special arrangement, and it was designed to teach the important lesson that, though we cannot with the eye of sense, see the throne of grace, we must "direct our prayer to it and look up" [Ps 5:3] (compare 2Co 3:14; Heb 10:20; Re 4:1).

JFB.