But why is it that good works cannot save us? Here are five answers to that question. First, good works can't cancel your sin but sin ruins your good works. Suppose you invite me over for breakfast one morning and offer to fix a three-egg omelet. As you begin to cook, I smell a putrid odor coming from the kitchen. What's that awful smell? Oh, it's just a rotten egg. But don't worry, I added a few good eggs that will cancel out the rottenness. Do you think I would eat your omelet? Not for a million dollars. Why? Because goodness doesn't cancel rottenness but rottenness ruins goodness. The same is true in the spiritual realm. You can’t be good enough to cancel out the putrid effect of your own sins.
Second, good works can't save you because God doesn't grade on a curve. He demands absolute perfection. If you understand the Bible, you know that it only takes one sin to send you to hell. Let's suppose that you somehow only committed three sins a day. That's impossible for most of us because we commit that many sins before getting out of bed in the morning. But let's give you credit for being very, very good. And let's further suppose that you never committed more than three sins a day for your entire life. That would be over 1000 sins a year, which would mean that in 70 years you would end up with over 70,000 sins on your record. Now let's further suppose that those sins were really speeding tickets. If a police officer stopped you for running a red light and discovered that you had 70,000 outstanding speeding tickets on your record, what would he do with you? You'd end up in jail so long they would throw away the key. Do you think God is any different? But you and I commit far more than three sins a day. Our sins are like a mountain-so high we can’t climb over it, so wide we can't walk around it, so deep we can't tunnel under it. Our sins are so great that our works could never save us.
Third, good works can't save you because you can never be good enough long enough. Just when you get a "good streak" going, you sin and have to start all over again.
Fourth, you can never be sure you've done enough. That's why most religious people have no assurance of their salvation. They truly believe that being good will get them to heaven. But as we've already seen, "doing good" is never good enough because we can never do enough to pay for our own sins.
There is one more answer to consider. Good works can't save you because if they could, you wouldn't need Jesus at all. Why would Jesus die on the cross if somehow you could save yourself? When we get to heaven, no one will be able to say, "You and me, Jesus, we did it together. I baked the cookies and you died on the cross." It's either all by Jesus or all by your own efforts – and nothing in between.