Christianity and Other Religions in Different Phases
There is an opinion that what Christ Jesus taught is not a religion that denies other religions:17 Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil.
18 For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled.
19 Whosoever therefore shall break one of these least commandments, and shall teach men so, he shall be called the least in the kingdom of heaven: but whosoever shall do and teach them, the same shall be called great in the kingdom of heaven. (Matthew 5)
If you are Judaists, Christians, Muslims, Buddhists, Hindus, Taoists, etc., you would have to admit that the earth goes around the sun, and the moon rotates around the earth. Understanding those facts does not hinder people from believing in any religion.
Likewise, understanding the truth Christ Jesus taught and presented should not hinder people from believing in any religion. Even Buddhists could accept the concept of the God held by followers of Christ Jesus: The creator and ruler of everything in this world and the spirit world.
So, it should be possible for a man believing in any religion to accept and believe in the truth Christ Jesus taught. A religion is deeply connected to a community or a society where a man was born or is living. Traditions, modalities, and rituals of religions are part of cultures of such communities. However, truth can be shared by any men believing in any specific religions.
Therefore, every no-nonsense religion is based on the notions that dead men live in an afterlife; pious men can be accepted in Heaven or the paradise while bad men are condemned to the hell; and there are holy spirits with deity and evil spirits with animosity against holy spirits.
Especially, the content and focus of the teachings of Christ Jesus are simple: After men's death, poor and pious men are welcomed in Heaven while rich and evil men fall down to the hell and are finally eradicated there.
Eventually, this core teaching is also the final end of any religions. It is because salvation of oneself is the final purpose for a man to believe in any religion. Even those who do not belong to any religion due to his fate or circumstances can accept this truth if they do not accept the religion of Christianity.
In addition, Christ Jesus only told to accept openly the truth he taught. He did not tell to do away with one's culture that includes any religion. So, it must be tolerated or accepted that a man confesses that he belongs to a certain religion by fate or due to the cultural tradition of his society but also believes in the truth Christ Jesus told like the truth the the sun rises in the east every morning.
In this context, it can be understood that Christ Jesus was a member of the Jewish society and thus a Judaist but also a believer of the truth He Himself proclaimed. So, any rituals and conditions involved in the religion Christianity might be a source of obstacles for acceptance of the truth just like traditions of the religion Judaism had become an obstacle for some Jewish people to accept the truth Christ Jesus had proclaimed.
Otherwise, we may as well think that the teaching of Christ Jesus was above the domain of religions, so that men of any religions can accept the teaching, since they belong to different phases.
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Romans 6, King James Version
12 Let not sin therefore reign in your mortal body, that ye should obey it in the lusts thereof.
13 Neither yield ye your members as instruments of unrighteousness unto sin: but yield yourselves unto God, as those that are alive from the dead, and your members as instruments of righteousness unto God.
14 For sin shall not have dominion over you: for ye are not under the law, but under grace.
15 What then? shall we sin, because we are not under the law, but under grace? God forbid.
16 Know ye not, that to whom ye yield yourselves servants to obey, his servants ye are to whom ye obey; whether of sin unto death, or of obedience unto righteousness?
17 But God be thanked, that ye were the servants of sin, but ye have obeyed from the heart that form of doctrine which was delivered you.
18 Being then made free from sin, ye became the servants of righteousness.