Question: "Why did God require animal sacrifices in the Old Testament?"
Answer: God required animal sacrifices so that mankind could receive forgiveness for their sins (Leviticus 4:35; 5:10). To begin, animal sacrifice is an important theme found throughout Scripture. When Adam and Eve sinned, animals were killed by God to provide clothing for them (Genesis 3:21). Cain and Abel brought sacrifices to the Lord. Cain's was unacceptable because he brought fruit, while Abel's was acceptable because it was the "firstlings of his flock" (Genesis 4:4-5). After the flood receded, Noah sacrificed animals to God. This sacrifice from Noah was an aroma that was soothing to the Lord (Genesis 8:20-21). God commanded Abraham to sacrifice his son Isaac. Abraham obeyed God, but just as Abraham was to sacrifice Isaac, God intervened and provided a ram to die in the place of Isaac (Genesis 22:10-13).
The sacrificial system reaches its climax with the nation of Israel. God commanded the nation to perform numerous different sacrifices. According to Leviticus 1:1-4, a certain procedure was to be followed. First, the animal had to be spotless. Next, the person offering the sacrifice had to identify with the animal. Then the person offering the animal had to inflict death upon it. When done in faith, this sacrifice provided forgiveness of sins. Another sacrifice called the day of atonement, described in Leviticus 16, demonstrates forgiveness and the removal of sin. The high priest was to take two male goats for a sin offering. One of the goats was sacrificed as a sin offering for the people of Israel (Leviticus 16:15), while the other goat was released into the wilderness (Leviticus 16:20-22). The sin offering provided forgiveness, while the other goat provided the removal of sin.
Why, then, do we no longer offer animal sacrifices today? Animal sacrifices have ended because Jesus Christ was the ultimate sacrifice. John the Baptist recognized this when he saw Jesus for the first time, "Behold, the lamb of God who takes away the sin of the world" (John 1:29). You may be asking yourself, why animals? What did they do wrong? That is the point, in that since the animals did no wrong, they died in place of the one performing the sacrifice. Jesus Christ also knew no wrong but willingly gave Himself to die for the sins of mankind (1 Timothy 2:6). Many people call this idea of dying in place of someone else substitution. Jesus Christ took our sin upon himself and died in our place. As 2 Corinthians 5:21 says, "He (God) made Him (Jesus) who knew no sin to be sin on our behalf, that we might become the righteousness of God in Him." Through faith in what Jesus Christ accomplished on the cross, the individual can receive forgiveness.
In summation, the animal sacrifices were commanded by God so that the individual could experience forgiveness of his sins. The animal served as a substitute--that is, the animal died in place of the sinner. Animal sacrifices have stopped with Jesus Christ. Jesus Christ was the ultimate sacrificial substitute and is now the only mediator between God and mankind (1 Timothy 2:5). Animal sacrifices foreshadowed Christís sacrifice on our behalf. The only basis on which an animal sacrifice could provide forgiveness of sins is the fact that Christ would sacrifice Himself for our sins, providing the forgiveness that animal sacrifices could only illustrate and foreshadow.