Once a year — only once — Aaron approached the golden incense altar with a different purpose. Targum Pseudo-Jonathan preserves the command that on the Day of Atonement, Yom Kippur, the High Priest would take the blood of the sin offering and touch it to each of the four horns of the altar. An expiation on the very altar that had borne incense all year (Exodus 30:10).
The sages heard something staggering in this. The altar that rose fragrance to heaven three hundred and sixty-four days a year needed, on the three hundred and sixty-fifth, to be cleansed. Even the closest vessel to the Holy of Holies accumulated the residue of Israel's imperfections. The incense had been offered with human hands, by human priests, on behalf of a human people. Something clung to the horns.
What did the horns represent?
In biblical Hebrew, keren means both "horn" and "power." The four horns of the altar faced the four directions — north, south, east, west — and the yearly atonement on each one was, in the rabbinic imagination, an atonement for Israel's failures in every direction of life. Public and private. Outward and inward. Seen and hidden.
This is why the verse concludes, "it shall be most holy before the Lord." The altar was not diminished by being cleansed. It was intensified. The yearly touch of blood was not a stain. It was a re-consecration — the horns drinking the atonement and rising again, ready for another year of fragrance.
The Maggid takes this home: even the holiest things in our lives need a yearly cleaning. The prayer that has grown stale. The practice that has grown automatic. Touch the horns with something honest once a year, and the altar lives again.