Men think that they are to be saved by keeping God’s commandments. They are to do their best, and they conceive that their sincere endeavors will be accepted, and they will thus save themselves. This self-righteous idea is diametrically opposed to the whole spirit of the gospel. The gospel is not for you who can save yourselves, but for those who are lost. If you can save yourselves, go and do it, and do not mock the Savior with your hypocritical prayers. Go and stumble among the tombs of ancient Israel, and perish as they did in the wilderness, for into rest Moses and the law can never lead you.
The gospel is for sinners who cannot keep the law for themselves, who have broken it, and incurred its penalty, who know that they have done so, and confess it. For such, a living Savior has come that he may blot out their transgressions. Seek not salvation by the works of the law, for by them shall no flesh living be justified. By the law is the knowledge of sin, and nothing more, but righteousness, peace, life, salvation, come by faith in the living Lord Jesus Christ, and by no other means. “Believe in the Lord Jesus Christ, and thou shalt be saved;” but if thou goest about to establish thine own righteousness, thou shalt surely perish, because thou hast rejected the righteousness of Christ.
From a sermon by Charles Haddon Spurgeon entitled "The Lord Is Risen Indeed," delivered April 13, 1873.