The bible doesn’t teach that there are multiple ways to the Kingdom of Heaven. In fact, it would be heresy for any Christian to say a thing. In John 14:6 Jesus actually said that he was the way, the truth, and the light and that no one goes through the father except through him. In John 10:1-16 he said that he was the “sheep gate” meaning that all of God’s sheep come to pasture through him, since only he is the good shepherd, it is only he that can protect the sheep.
In John 11:22-27, when Jesus was talking to Martha about raising the deceased Lazarus, she said “But even now I know that God will give you whatever you ask” in verse 22. In verse 27 she confirms that she believed that Jesus was the Messiah, and this reveals why she believed God would give him anything he wants. In Matthew 26:53, Jesus even told Pontius Pilate that he could ask for a legion of angels to come and rescue him and God would send them. It is clear that the bible implies that Jesus was so precious to God that he could ask for anything and the father give it to him. So, when Jesus asked God if he is willing to remove this cup (referring to his crucifixion) in Luke 22:42, why didn’t the father remove it? If God loved his son so much that he would give anything, then why didn’t he make another way for people to be saved, so that he could spare Jesus this cup of suffering (John 18:11)? It is because there was no other way, and this was something that had to be done. If there were other methods of salvation that didn’t involve Jesus dying for us, then God would have used those in order to spare his son, as he asked.
The Promise of salvation was made right after the fall in Genesis 3:15. God promised a man or “seed” would come from the woman (women don’t have “seeds” so many believe this is a reference to virgin birth), to bruise the serpent’s (Satan’s) head and in return, the serpent would bruise the man’s heel. This promise of the sacrifice for all of humanity by a second, perfect human, like Adam, was made from the beginning. This implies that there was never truly another way to undo the corruption that resulted from Adam’s failure to keep God’s covenant. Throughout scripture, we see references to the one of suffers for our sins (Psalm 22, Isaiah 53, etc). The cost of sin is death (Rom 6:23). Someone who was like Adam, the man that broke the covenant, had to pay the price and Jesus is the only one that was ever made pure from birth like Adam. If there was another way God would have done it because he loved Jesus, but there wasn’t so he did what had to be done, even though Jesus asked for an alternative.
To suggest that there was another way this whole time is to suggest that God is incompetent and that he killed Jesus for no reason. Plus the promise of God pouring out the Holy Spirit to transform our hard hearts is in vain since only Jesus promised him (John 14:15-17, John 16:5-15) and we never needed him. If we can save ourselves and receive eternal life by just following the Torah or generating good Karma, then we have no need for a savior or God’s spirit, and following Christ has no value.