From the book "Mere Christianity", buy C.S. Lewis. Page 148-149, the second chapter on Faith:
"Christians have often disputed as to whether what leads the Christian home [Heaven] is good actions, or Faith in Christ...Faith in Christ is the only thing to save you from despair at that point: and out of that faith in Him good actions must inevitably come. There are two parodies of the truth which different sets of Christians have, in the past, been accused by other Christians of believing: perhaps they may make the truth clearer. One set were accused of saying, 'Good actions are all that matters. The best good action is charity. The best kind of charity is giving money. The best thing to give money to is the Church. So hand us over $10,000 and we will see you through.; The answer to that nonsense of course, would be that good actions done for that motive , done with the idea that Heaven can be bought, would not be good actions at all, but only commercial speculations. The other set were accused of saying, 'Faith is all that matters. Consequently, if you have faith, it doesn't matter what you do. Sin away, my lad, and have a good time and Christ will see that it makes no difference in the end.' The answer to that nonsense is that, if what you call your 'faith' in Christ does not involve taking the slightest notice of what He says, then it is not Faith at all - not faith or trust in Him, but only intellectual acceptance of some theory about Him. The Bible really seems to clinch the matter when it puts the two things together into one amazing sentence. The first half is, 'Work out your own salvation with fear and trembling' - which looks as if everything depended on us and our good actions: but the second half goes on, 'For it is God who worketh in you' - which looks as if God did everuthing and we did nothing."