When God placed Adam and Eve in the Garden of Eden, he said they could have anything they wanted except from one particular tree. They disobeyed and ate the forbidden fruit. In shame, they covered their nakedness with leaves while hiding from God. When he came upon them, he replaced those leaves with the skin of animals. In doing so, blood was shed for their disobedience. God’s original plan was for mankind to have a relationship with him. However, they had the means to disobey, but not the means to rectify what they did. The answer was for something or someone to shed blood to cover their rebellion that severed the relationship with him. After being expelled from the Garden of Eden, shedding of animal blood became part of their worship.
Their two sons followed this example. Abel sacrificed an animal, but Cain attempted to go back to offering plants to God that was that was the result of human effort to worship God. This is what Adam and Eve tried to do that was unacceptable to God. In other words, God will not accept any old way to seek him but the only way that he established. The worship of God had to include the shedding of blood as instituted by God, not by some method through human self-will. The shedding of blood was an example of God’s intervention for human sin. Nothing else was acceptable. It was a contract between God and man for their redemption.
After Moses led the Hebrews out of their four-hundred-year captivity in Egypt, God gave them a set of laws which included animal sacrifice. It continued for many years as they possessed the promised land that is now called Israel. Even at the time of Jesus, animal sacrifice was practiced. However, God planned through Jesus to provide the ultimate perfect sacrifice by the death of Christ on the cross for the sins of all mankind. All those sacrifices in faith of animals pointed toward Jesus even though they did not realize it. Animals did not have the ability to exercise free will. Therefore, because Jesus had free will, he freely gave himself on behalf of all sinners to be reconciled to God. That means he was the only and ultimate sacrifice for mankind.
Animal sacrifice continued until 70 A.D. when the Roman general Titus sacked the city of Jerusalem and destroyed the Temple. Jews scattered throughout the world without a homeland, without a place to worship, and without a means to offer sacrifices. They rejected the sacrifice of Jesus on the cross as their Messiah. To this very day they have no Temple. All that remains of the original Temple is a wall where modern Jews go to pray. They write notes as part of their prayer sticking them in the crevices between the blocks of stone.
That ancient destruction of their homeland, and the rejection of Jesus as the Messiah, left the Jews unable to fully practice worship. As time evolved, they concluded that it was necessary for them to develop their own individual way to appease God for sin. That included the rejection of the original teaching of the Messiah as a person. Their current theology states that the human soul after death of the physical body is recycled into future bodies so that they may eventually become the individuals that would be more acceptable to God.
According to Romans 11, by the Jews rejecting Christ it became possible for the Gentiles to be grafted into the plan of salvation as a branch is grafted into the healthy vine. In the end, God looks toward the redemption of the Jews with the Gentiles (non-Jews) to be his own. But Jews and Gentiles continue to reject Jesus for reconciliation with God.
Currently those who do accept Jesus as their Savior, are called Christians or believers. Many offshoots of Christianity have grown proportionally seeking any possibility to replace faith in Christ favoring instead human practices and self-will. Generally speaking, they are referred to as cults. It is wise not to become involved in any alternative because it is a form of rebellion. It is so curious how people seek anything other than Jesus. He is the only One who died and also rose from the grave while everything else is good works and some form of philosophy. Those other ways say to be good enough and everything else would be okay. If you were God, would you accept any dreamed-up method when you already had established the way?
This is why Christian teaching from the Bible says that Jesus is the only way to heaven. He is the only perfect sacrifice shedding his blood consistent with what God did for Adam and Eve in the Garden of Eden. No matter what doctrine anyone follows, if it does not include faith in the redemptive work of Christ, that doctrine is not consistent with God’s plan. The effective answer is for anyone to once again exercise free will, not by rejecting God, but by choosing to have faith in Christ, as the only sacrifice for sin, and then live a life pleasing to God that is consistent with Scripture. We still have freewill to accept or reject God, but acceptance can only be through Christ. Bear in mind that Jesus is God incarnate. He came from heaven so that all of us might have redemption.