Exodus 30:10

And Aaron shall make an atonement upon the horns of it once in a year with the blood of the sin-offering of atonements; once in the year shall he make atonement upon it throughout your generations, namely, on the great Day of Atonement; it is most holy unto the Lord. The altar of incense thus served a double purpose: it was in use daily for the offering of incense, the aromatic substance whose odor was pleasant to the Lord, since it signified the prayer of the saints; and it served on the great Day of Atonement for the dedication of the blood of expiation, before the high priest entered the Most Holy Place. We Christians also let our prayers rise to the Lord like incense, that is, in the name of Jesus Christ the Savior, knowing that they are pleasing to the Lord for His sake.