Here is where a 50-50 probability has to be accepted. Suppose, I believe in the existence of hell and hence, I do not commit sins. Even if, after my death, I find out that there is no hell, there is no loss for me. While I am still alive, I have already enjoyed the benefit of living a tension-free life and not having to bother about the police and courts, since I have not committed any sins. On the other hand, if you commit sins believing that hell does not exist and after your death, if you find out that unfortunately, hell does exist, you are totally lost!
So, whenever there is a 50-50 probability, a wise man always errs on the safe side. One must always choose the side with a lower risk. Let us say there is a blind person walking on the road. One person tells him that there is a fire ahead in his path and another person tells him that there is no fire ahead. Whom should the blind man choose to follow?
Certainly, if he is a wise blind man, he will turn back because even if the fire is absent, there would be no loss to him. But if the blind man is foolish, he will choose to disregard the warning and take the risk of going forward. If unfortunately, there is actually a fire ahead, he will get burnt!
Therefore, choose the side of lower risk given the 50-50 probability and believe in the existence of the unimaginable God, heaven and hell. Worship God with devotion and do meritorious deeds without committing any sins. Even if God, heaven and hell are absent, you will get enough benefit of believing in God, heaven and hell, which is a life of happiness, peace and freedom from even a trace of tension of the police and the courts.
After all, whether a person is a theist or an atheist, all the efforts the person makes in life is only to get this benefit of a peaceful and happy life. Apart from this benefit in this world, there is also the possibility of you getting a huge benefit in the upper worlds after your death, which is very clearly stated by several Godmen and divine scriptures.
If the atheist leads a worldly life following justice and avoids sins (pravṛtti), it is more than sufficient. Devotional life (nivṛtti) is not mandatory for him. But accepting at least the existence of the unimaginable God is essential for everybody because it controls sins by instilling the fear of punishment from God. God and His ways of punishment being unimaginable, one can never escape from them, even though one might be able to escape from the police and the courts in this world. The concept of the Human Incarnation is not necessary for an atheist. The atheist should also have open mind to observe the genuine miracles in this world. The observed genuine miracles are essentially unimaginable events and they prove the existence of their source, who is the unimaginable God. The concept of the Human Incarnation is only essential for nivṛtti, which is the path chosen by devotees who aspire for the extreme grace of God.