The LORD spoke to Moses after two of Aaron's sons had died. They were the sons who died when they came near the Lord.
References for Leviticus 16:1
The LORD said to Moses, "Speak to your brother Aaron. Tell him not to come into the Most Holy Room just anytime he wants to. Tell him not to come behind the curtain that is in front of the cover of the ark. The cover is the place where sin is paid for. If he comes behind the curtain, he will die. That is because I appear in the cloud over the cover.
"Aaron must not enter the area of the sacred tent without bringing a sacrifice. He must bring a young bull for a sin offering. He must also bring a ram for a burnt offering.
"He must put on the sacred inner robe that is made out of linen. He must wear linen underwear next to his body. He must tie the linen belt around him. And he must put on the linen turban. Those are sacred clothes. So he must take a bath before he puts them on.
"The community of Israel must give him two male goats and a ram. The goats are for a sin offering. The ram is for a burnt offering.
"Aaron must offer the bull for his own sin offering. It will pay for his own sin and the sin of his whole family.
"Then he must take the two goats and bring them to me at the entrance to the Tent of Meeting.
He must cast lots for the two goats. One lot is for me. The other is for the goat that carries the people's sins away.
Aaron must bring the goat that is chosen for me by lot. He must sacrifice it for a sin offering.
"But the goat that is chosen by the other lot must remain alive. First it must be brought in to me to pay for the people's sin. Then it must be sent into the desert as a goat that carries the people's sins away.