Introduction to the Day of Atonement

Leviticus 16:1-2

And the Lord spoke to Moses, after the death of the two sons of Aaron when they were slain upon their offering strange fire:

And he commanded him, saying: Speak to Aaron thy brother, that he enter not at all into the sanctuary, which is within the veil before the propitiatory, with which the ark is covered, lest he die, (for I will appear in a cloud over the oracle),