I received the question in the title, and my response is below:
The truth of Christianity comes down to the resurrection. If Jesus was raised from the dead then it seems God has endorsed Jesus and thus Christianity. If Jesus was not raised from the dead, then he is just another failed messianic pretender from the 1st century who came to an ignoble end. Reasonable faith has put out a couple of short videos which I have linked below that provide evidence for the claim that Jesus was raised from the dead. The first two are shorter videos and the third is a longer one if you have the time.
In terms of a Christian Cosmology, Genesis chapters 1-11 really provide the Jewish and Christian cosmologies. For a more thorough analysis I would take a look at the Defenders Podcast by William Lane Craig, which covers these things in great detail.
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