Jesus showed something in a parabel... and it is important to understand what he was telling:
"A certain man was going down from Jerusalem to Jericho, and he fell among robbers, who both stripped him and beat him, and departed, leaving him half dead. By chance a certain priest was going down that way. When he saw him, he passed by on the other side. In the same way a Levite also, when he came to the place, and saw him, passed by on the other side. But a certain Samaritan, as he travelled, came where he was. When he saw him, he was moved with compassion, came to him, and bound up his wounds, pouring on oil and wine. He set him on his own animal, and brought him to an inn, and took care of him. On the next day, when he departed, he took out two denarii, and gave them to the host, and said to him, 'Take care of him. Whatever you spend beyond that, I will repay you when I return.' Now which of these three do you think seemed to be a neighbour to him who fell among the robbers?" He said, "He who showed mercy on him." Then Jesus said to him, "Go and do likewise."
According to Jesus it was not the priest or the levite who was doing the right thing... it was the Samaritan (not a direct follower of Christ or of the TRUE religion) who was doing what he should do...
Moral of the story: You probably can be "wrong" with the beliefsystem and STILL do what you should do!
Putting it some other way: There is NO way for us people in the world to be able to get to see the WHOLE and REAL truth! How could we since bibles and theologies are corrupt... there are gazillions of religions... there is no way to get to a beliefsystem that is doing the right thing all the time! The only LAW that we CAN follow BLINDLY is the law of love...
Let me take the illustration of the Samaritan and put some other conversations in it:
The levite and the priest come home and tell them what they saw: they saw a brother lying on the street and they told some friends and say: tell ya what! some guy was lying on the street and was dying there but I could not stop because I was attending a meeting of priest and had to make a sacrifice anyways. God loves me because I am doing his will...
They did not understand that the law of LOVE was more important then the religious system... and we see that all day every day.
So who does truly believe? Who does truly show faith? I think it is those that show other people that they love other humans... it is the only faith we do not have to doubt