Well, all the atheists in here seem to forget a few things (not really surprising, seeing as they are mostly either strawmanning, or picking on some obscure Protestant branches I know nothing about), but I would like to point to some of them at least:
a) Catholic Church believes not only Bible itself, but also Tradition (yeah, capital T) is basis for outside forms; most importantly, stuff like going to church every Sunday is not explicitly mentioned in Bible, but it is part of the Tradition, descending from Apostoles, who knew a lot about Jesus and his teachings (this is also why their letters are a part of New Testament). Protestants are less interested in Tradition, as far as I know (but I might be mistaken here).
b) Because heaven is eternal and perfect, going to heaven is worth even the greatest pains in one's earthly existence. Heaven is infinity; mortal life is finite. No matter how big finite number you subtract from infinity, it doesn't change; the result is still infinity. Thus, pain and suffering in mortal life that leads to being a better person and landing in heaven is worth it, no matter how much pain and suffering.
c) God is omniscient and all-powerful; but He chose to give us free will, thus sacrificing a part of of His power. He is still all-powerful, but He doesn't exercise His powers to make our will really free. We can choose whether to believe Him or not, whether to be good or not, et cetera. Because blessed are those who have not seen, yet believed. It is nothing noteworthy if you know that God exists, because every morning He writes 'Hello' in burning letter on the sky when you go to work, to believe.
d) Where do the morals come from, if there is no God? Who is to say that killing is wrong, and helping poor is good, and not vice-versa? Who says that you can eat oatmeal, and can't eat human flesh?