John Calvin Commentary Exodus 30:10

"And Aaron shall make atonement upon the horns of it once in the year; with the blood of the sin-offering of atonement once in the year shall he make atonement for it throughout your generations: it is most holy unto Jehovah." — Exodus 30:10 (ASV)

And Aaron shall make an atonement. We should observe here the correspondence between the two altars. For, as the Israelites were admonished that the sacrifices would not please God unless all uncleanness were wiped away by pure and holy prayers, so also the altar of incense was purified by the sprinkling of blood, so that they might learn that their prayers obtained acceptance through sacrifices.

Although this was only done once a year, yet it was to be called to mind daily, so that they might offer the death of Christ by faith and prayer,¹⁵³ and yet might know that their prayers had no sweet savor unless they were sprinkled with the blood of atonement.

¹⁵³ “Ut fide et precibus adolerent mortem Christi.” —.” — Lat. “Afin qu’en appliquant a eux la vertu de la mort de Jesus Christ par foy et prieres;” in order that applying to themselves the virtue of the death of Jesus Christ by faith and prayers. — ;” in order that applying to themselves the virtue of the death of Jesus Christ by faith and prayers. — Fr.