"If you could lose your salvation, you would. You understand that? If you could, you would. If it's possible, it will happen. It has to be. If any part of my eternal salvation depends upon my power and ability and commitment and righteousness, I won't get there. Think about Adam. Adam who had no sinful tendencies, Adam living in a perfect world wouldn't know sin. No sin at all. Adam with no sin at all and no sinful tendencies inside couldn't keep himself in a right relationship of obedience and love to God. How would we think we could in a fallen world with fallen natures? And the more mature you are as a Christian, the more spiritually minded you are, the more righteous you are, the more sanctified you are, the more wretched you know you are, right? The Apostle Paul in Romans 7, 'O wretched man that I am,' that's the statement of a very mature Christian ... Spurgeon said, 'No man can keep himself, he'll surely fail. If left to ourselves, we'll go to hell. Only Jesus can save us from our sins.'"
John MacArthur, "The Saint's Guarantee"