Exodus 30:10

Once a year Aaron is to make atonement on the horns of the altar. Every year, for all your generations, he will make atonement on it. He will use the blood of the sin offering for atonement. The altar is most holy to the LORD."

Exodus 30:10, Readable English Bible (READ)

Note: Atonement means covering or paying for sin so people can be right with God.