Leviticus 16:11

"And Aaron shall present the bullock of the sin-offering, which is for himself, and shall make atonement for himself, and for his house, and shall kill the bullock of the sin-offering which is for himself: and he shall take a censer full of coals of fire and from off the altar before Jehovah, and his hands full of sweet incense beaten small, and bring it within the veil: and he shall put the incense upon the fire before Jehovah, and the cloud of the incense may cover the mercy-seat that is upon the testimony, that he die not: and he shall take of the blood of the bullock, and sprinkle it with his finger upon the mercy-seat on the east; and before the mercy-seat shall he sprinkle the blood with his finger seven times."

"That the cloud of incense may cover the mercy-seat ..." "This did not cover the `glory' that Aaron might not gaze upon it, but it covered him that Jehovah might not look upon him and his sin!"[23]

Aaron's entering into the supreme sanctuary, the Holy of Holies to sprinkle the blood upon the mercy-seat symbolized the entry of Jesus Christ, our High Priest, into heaven itself, the Most Holy place indeed, there to offer his blood once for all for the cleansing and forgiveness of sins. That it was "within the veil" means that Christ offered his blood in heaven, after he passed through the veil of death. (See Hebrews 8-10 for remarkably full discussion of all the analogies here.)