Know yourself

Labour to see the emptiness, shortness, and the pollution that cleaveth to a man's own righteousness.  This also must in some measure be known, before a man can know the nature of the love of Christ.  They that see nothing of the loathsomeness of man's best things, will think, that the love of Christ is of that as to be procured, or won, obtained or purchased by man's good deeds.  And although so much gospel light is broken forth as to stop men's mouths from saying this, yet 'tis nothing else but sound conviction of the vileness of man's righteousness, that will enable men to see that the love of Christ is of that nature, as to save a man without it; as to see that it is of that nature as to justify him without it:  I say, without it, or not at all.  There is shortness, there is hypocrisy, there is a desire of vain glory, there is pride, there is presumption in man's own righteousness: nor can it be without these wickednesses, when men know not the nature of the love of Christ. 

-John Bunyan, All Loves Excelling, p. 85.