Sometimes stuff just happens. People can get better from serious illness without explanation of medical science. 999.99/1000 times though, people can pray to whomever they please as hard as they like, and they will still die from the cancer (that 'god' presumably gave them)
Unfortunately the idea that God is performing a miracle is akin to the ideas that the ancient greeks once had, in that when ever something good happened it was because of a specific gods graces. The difference with that and christianity is that the greeks also had bad gods that did bad things. Because of the way christanity is structured, the people who follow it are meant to both fear and love their god, so he is the good cop and the bad cop.
The people who invented christianity as a method of checks and balances on society were brilliant in their assunmptions that people would fall for this form of organised religion, and saw a decent penny to be made.
That is why new religions and religeous cults to this day are still able to trick people into surrendering their time, liberties and money.
Christians also need to understand that people can be charitable, nice and live by the moralities that were around long before christianity was invented, and which christianity is based upon. If there were no religion, god or churches, groups of people would still gather, and people would give to the poor and help others.
To be honest the world probably would have advanced a lot quicker without god getting in the way of progress for all the middle ages, where to world saw a massive regression.