First, a good work is a work performed in obedience to the Law of God. A good work is not a work which society classes as "good." A good work is not a work which makes another person happy. A good work is a work which is in harmony with God's will as that will is revealed in His Law. That Law is summarised in the Ten Commandments. To obey the Ten Commandments means more than outward obedience. Jesus made that very clear in His famous Sermon on the Mount. A man is guilty of murder when he hates another person in his heart and when he curses him with his mouth; a man is guilty of adultery when he lusts after another woman in his heart (Matt. 5:21-28). If that is the standard, our ability to do good works by obeying God's Law begins to look very uncertain. In fact, it is worse than that: it is impossible for us to do good works by nature. The Word of God says, "The carnal mind is enmity against God [hostile towards God] for it is not subject to the law of God, neither indeed can be" (Rom. 8:7).
Second, a good work is a work from a good source, namely faith. Jesus speaks about two different kinds of people as two different kinds of trees. A bad tree cannot produce good fruit. First, He says, make the tree good and then it will produce good fruit. We are all evil trees! As evil trees we produce only evil fruit! (Matt. 7:16-20). The Word of God also says that "whatsoever is not of faith is sin" (Rom. 14:23). This means that whatever an unbeliever does, even if he is praised to the skies by society, is sin, not a good work! Unbelieving movie stars, rock singers, politicians who give to the poor, who alleviate suffering, who work for the good of mankind are sinning! Does that mean that it would be better for them to ignore the poor, cause suffering and destroy society? No, of course not. That would be greater sin. The point is: whatever an unbeliever does is sin, and when an unbeliever neglects to perform outwardly moral acts he sins even more. But, he never produces even one good work which he can place on one side of the heavenly scale.
Third, a good work is a work aimed at the glory of God. The word "sin" in the Bible means a "missing of the mark." The mark (the goal) of life must be the glory of God. But, we sinners aim in an entirely different direction. Sinners refuse to aim at the glory of God. To aim at the glory of God is consciously to seek that in all things by our thoughts, words and deeds God would be praised. It means that we do not seek our own glory. It means we do not seek the approval of men. It means that the good of our neighbour is secondary to the glory of God. "Whether therefore," says the Bible, "ye eat or drink or whatsoever ye do, do all to the glory of God" (I Cor. 10:31).
So, if that is the standard for good works, how many good works have you performed?
But, what about the good works of Christians, of those who really do love God, and really do believe in Jesus Christ and who really are sorry for their sins? Do they not do good works?
They do, but, remember, even their good works are imperfect. How much pride, selfishness and other sins attach themselves to and are mixed with our best works?
That is why good works, even the good works of the best Christian, can never make anyone acceptable to God and earn us God's favour and a place in heaven. "By grace are ye saved through faith; and that not of yourselves: it is the gift of God, not of works, lest any man should boast" (Eph. 2:8-9).