Give some reason why it is important for catholics that non-christians sources validate that jesus really existed

Because, Christians already like given their faith to belive in Jesus Christ, but if he's not real, then that would be tragic They want to have someone to belive in that could make their lives better and take care of them in the "afterlife" if there is one. Non believes don't really care since they already kinda know he's not real If today's the were to find out, there would be more Christians then ever.

Baiscaly more Christians+no Jesus=less Christian believes

Non believes + a Jesus = more Christians