Who said religion was irrational?
Proposition 1: You cannot disprove the existence of an eternal heaven and hell. The most you can do is say is that it is ‘unlikely’.
Proposition 2: Every human will die, hence happiness in this world is finite.
Proposition 3: Every human being seeks to maximise their own happiness.
Conclusion 1: The cost of believing in and acting for heaven is finite as life itself if finite.
Conclusion 2: Maximising your happiness is done by working towards a hereafter and not this world as both the infinite reward of heaven and the punishment of hell are greater than any cost one could sacrifice in this world, regardless of how improbable they are.