The first part is a response to “why would somebody be sad if their religion turned out to be false”, which for the record, if you need it explained to you why that might be, you’re really earning that “edgy teenager” label.

The second is saying that there’s literally no way to be sure of answers on the scale of “is there a god?”, science included

Philosophy asks some “why?” questions, but if you think it’s equipped to definitively answer all of them you don’t know much about philosophy.