It’s very hard to derive the idea from the Bible that good works save a person from his sins. Scripture is very clear that we are saved only by grace through the righteousness of Christ. The idea of salvation by grace alone through faith alone was bitterly opposed by the Roman Catholic Church during the Reformation. The Catholic reasoning said that if good works were not required for salvation, there would be nothing to hold over the heads of people to motivate them to do good. This is exactly opposite of the teaching of the Bible. Scripture says that good works flow naturally from a heart than has been regenerated. Paul rejects the idea that salvation by grace produces lawlessness (Rom. 6:1). Instead, says Paul, it ought to produce a desire to please God unlike anything before that was motivated by guilt or fear.
On the other hand, there are those who believe that once a person is saved, he can exhibit no spiritual fruit, that is, no evidence of salvation. The apostle John rejects this idea throughout his first epistle.
The Sermon on the Mount causes many to stumble because it seems to teach works salvation. But the point of the Sermon on the Mount is that genuine believers will practice good works as a result of their regenerated hearts. Herman Ridderbos explains this eloquently:
What Jesus thus requires is that men reflect the light which they received from Him. The endowment of the Kingdom accomplishes good works in its recipients, and thus the Kingdom finds embodiment in the lives of the faithful.
(When the Time Had Fully Come, Grand Rapids: Eerdmans, 1957, 31)
So, is the light of Christ being reflected in our lives? If not, maybe there is no light! And if we are truly converted, good works, such as those described in the Sermon on the Mount, ought to be ever-increasing in our lives.