Does God really require the sacrifice of blood for the atonement of sins?

      Yes, God requires the shedding of blood as a sacrifice for the atonement of sin (Hebrews 9:22), along with burnt offerings of perfect animals as consecration of what is holy and for other gifts that are pleasing to him. Not to go in-depth into the theology of the shedding of blood, the main reason was that through sin came death and those who sinned died in their sins. But the innocent blood of the blameless could be substituted for the sins of the guilty, though not the blood of an innocent man since this was a sin in itself, so a clean animal (those acceptable for eating) without blemish was required.

        When Moses had proclaimed every commandment of the law to all the people, he took the blood of calves, together with water, scarlet wool and branches of hyssop, and sprinkled the scroll and all the people. He said, "This is the blood of the covenant, which God has commanded you to keep" [Exodus 24:8]. In the same way, he sprinkled with the blood both the tabernacle and everything used in its ceremonies. In fact, the law requires that nearly everything be cleansed with blood, and without the shedding of blood there is no forgiveness. (Hebrews 9:19-22)

      The general requirements for the burnt offering, as recorded in Leviticus 1, were for each individual to bring either a sheep, goat, bull, dove, or pigeon without defect to the temple and lay their hand on the head as the animal was slaughtered, the blood of which was sprinkled on the altar by the priest and the meat and fat burned on the altar as "a burnt offering, an offering made by fire, an aroma pleasing to the Lord" (Leviticus 1:17). Not only was the offering for the atoning of sin and to take away God's wrath, but the aroma of the burnt offering was pleasing to him (Genesis 8:20-21, Ephesians 5:2).

      Following are the reasons for the various animal sacrifices as commanded by the Lord to his people Israel.

      Passover (Exodus 12), a feast to be celebrated by sacrificing a lamb in remembrance of God passing over all Israelites in Egypt who had the blood of a lamb sprinkled on their doorway so that the angel of the Lord would not kill their firstborn, both children and animals. This is held beginning on the fourteenth of the first month (Numbers 28:16-25, Deuteronomy 16:1-8). Even Jesus, the sacrificial lamb himself (John 1:29, 1 Corinthians 5:7, 1 Peter 1:19, Revelation 5:6-14), obeyed God's commands and participated in the Passover (Mark 14:14, Luke 22:8).

      Other celebrations requiring burnt offerings included the Feast of Weeks (Numbers 28:26-31), Feast of Trumpets (Leviticus 23:23-25, Numbers 29:1-6), Day of Atonement (Leviticus 23:26-32), Feast of Tabernacles (Leviticus 23:33-38, Numbers 29:12-40), and Feast of Firstfruits (Leviticus 23:9-14).

      Consecration of the Priests (Exodus 29, Leviticus 16), a young bull and two rams without defect were to be slaughtered and their blood sprinkled on everything that would be in the temple, including the priests and the altar, to make them holy. The fat and flesh of the animals were also burned on the altar as "a burnt offering to the Lord, a pleasing aroma, an offering made to the Lord by fire" (Exodus 29:17). Christ himself was consecrated by his own blood to enter the temple in heaven (Hebrews 9:11-14).

      Consecration of the Firstborn (Exodus 13:11-16), in remembrance of the Lord killing every firstborn male in Egypt (both man and animal), everyone was to sacrifice their firstborn animals in redemption of their firstborn children.

      Fellowship Offering (Leviticus 3, 7:11-21), a peace offering to the Lord requiring the shedding of blood and a burnt offering of an animal without defect. Similar sacrifices include the freewill and thank offering, dedicated to the Lord of an individual's own free will out of gratitude for the Lord's blessings and abundance.

      Sin Offering (Leviticus 4, 6:24-30, Numbers 15:22-29), for unintentional sins, whether by the priests, the community, or the leaders, was a burnt offering covering the sins of the people as a whole to take away their guilt (whether they knew of the sin or not). Intentional sins, those done in defiance to blaspheme the Lord, were not covered by atonement of a sacrifice, but the individual was unforgiven and either cut off from the community (Numbers 15:30-31) or put to death (Leviticus 24:10-23). Sabbath-breakers were also stoned to death (Numbers 15:32-36). Much the same way as the remains of the sin offering were burned outside the camp, the body of Jesus was buried outside the city (Hebrews 13:11-14).

      Guilt Offering (Leviticus 5:14-19, 7:1-10), a burnt offering along with a monetary amount, was for the atonement of guilt brought on by an unintentional sin by a community member as failure to do what was holy.

      Daily Offering (Numbers 28:1-8), a general daily offering of two lambs without defect -- one in the morning and one in the evening. This was also to be offered every Sabbath day (Numbers 28:9-10) and on the first of each month, along with a goat as a sin offering (Numbers 28:11-15).

      The first offering accepted by God was from Abel in Genesis 4:4, although it wasn't commanded. This was symbolic in many ways to the subsequent commands of the Lord for animal sacrifices; including the shedding of Abel's innocent blood, the offering of firstfruits, and the freewill offering.

        When they become aware of the sin they committed, the assembly must bring a young bull as a sin offering and present it before the Tent of Meeting. The elders of the community are to lay their hands on the bull's head before the Lord, and the bull shall be slaughtered before the Lord. Then the anointed priest is to take some of the bull's blood into the Tent of Meeting. He shall dip his finger into the blood and sprinkle it before the Lord seven times in front of the curtain. He is to put some of the blood on the horns of the altar that is before the Lord in the Tent of Meeting. The rest of the blood he shall pour out at the base of the altar of burnt offering at the entrance to the Tent of Meeting. He shall remove all the fat from it and burn it on the altar, and do with this bull just as he did with the bull for the sin offering. In this way the priest will make atonement for them, and they will be forgiven. Then he shall take the bull outside the camp and burn it as he burned the first bull. This is the sin offering for the community. (Leviticus 4:14-21)

      There are some who argue that the Israelites were primitive and made up these rituals out of ignorance, however, they were rituals set forth by God to Moses as part of the law, and were adhered to out of fear of God's wrath (Exodus 8:20-12:33) and in the face of opposition (Ezra 3:1-6). God even told Job's friend, Eliphaz, to sacrifice burnt offerings to him because of their ignorance of the Lord (Job 42:7-8). In later times, the prophets warned that the sacrifices of the people were lacking (Isaiah 43:22-24) and unacceptible because not only the animals, but their hearts, were imperfect (Malachi 1), and also that their obedience to the Lord was of more importance and their offerings worthless without it (1 Samuel 15:22, Psalm 40:6-8, 51:16-19, Proverbs 21:3, Isaiah 1:10-17, 66:3, Jeremiah 7:21-24, Hosea 6:6, Mark 12:33) -- but never that their sacrifices were done out of ignorance of God's commands (Psalm 50:8). Sacrificial offering was one of the main reasons for building God's temple in Jerusalem, and by his very own specifications (1 Kings 6:11-13, 8:62-64, 2 Chronicles 7:12, Ezra 6:3, Ezekiel 40:38-43, 43:18-27, 44:15), and it is also the reason for God's spiritual temple in the bodies of believers in Christ (1 Peter 2:5).

        "This is what the Lord Almighty, the God of Israel, says: Go ahead, add your burnt offerings to your other sacrifices and eat the meat yourselves! For when I brought your forefathers out of Egypt and spoke to them, I did not just give them commands about burnt offerings and sacrifices, but I gave them this command: Obey me, and I will be your God and you will be my people. Walk in all the ways I command you, that it may go well with you. But they did not listen or pay attention; instead, they followed the stubborn inclinations of their evil hearts. They went backward and not forward." (Jeremiah 7:21-24)

      Although it was never the Lord's intent for men to sacrifice people to him (Genesis 22:1-14, Jeremiah 32:35), he did offer his Son as a sacrifice of sin for all the world (Romans 3:25, 1 Corinthians 5:7, Ephesians 1:7, 5:2, 1 John 2:2, 4:10), through redemption by the shedding of his innocent blood (Matthew 26:28). The sin sacrifices of the priests of the law could never actually take away sin, but the shedding of the blood of Jesus was the sacrifice that did once for all (Hebrews 9:25-10:18). And Jesus himself upheld the sacrifices of the Old Testiment (Mark 1:43-44, Luke 5:14), but put an end to them on the cross by replacing them with his own body and blood, the ultimate sacrifice (Isaiah 53:5, Romans 5:8, 1 Corinthians 15:3, Galations 3:13, Colossians 1:19-20, 2:13-14, Hebrews 9:15, 1 Peter 3:18).

        First he said, "Sacrifices and offerings, burnt offerings and sin offerings you did not desire, nor were you pleased with them" (although the law required them to be made). Then he said, "Here I am, I have come to do your will." He sets aside the first to establish the second. And by that will, we have been made holy through the sacrifice of the body of Jesus Christ once for all.
        Day after day every priest stands and performs his religious duties; again and again he offers the same sacrifices, which can never take away sins. But when this priest had offered for all time one sacrifice for sins, he sat down at the right hand of God. Since that time he waits for his enemies to be made his footstool, because by one sacrifice he has made perfect forever those who are being made holy.
        The Holy Spirit also testifies to us about this. First he says: "This is the covenant I will make with them after that time, says the Lord. I will put my laws in their hearts, and I will write them on their minds" [Jeremiah 31:33]. Then he adds: "Their sins and lawless acts I will remember no more" [Jeremiah 31:34]. And where these have been forgiven, therer is no longer any sacrifice for sin.
(Hebrews 10:8-18)