Robert Traill (The Throne of Grace), Works 1:124:
To come for mercy in faith, is to believe the fitness and suitableness of God’s mercy to our misery. Here many stumble woefully. Their question is, “Am I fit for mercy?” when it should rather be, “Is his mercy fit for me?” And this question every sensible soul can answer; the other none in heaven or earth can answer. If any man think himself fit for mercy, of all men, that man is most unfit for it, and farthest from receiving of it. But every sensible soul will say, “Though I be unfit for, and unworthy of mercy; yet mercy is very fit for me. Is there pardoning mercy with God? who is it so fit for as a guilty vile sinner? Is there saving mercy with him? who is it so fit for as for a lost man, as I am?” Come to the throne of grace for mercy, in faith of this, “Mercy is fit for me exactly, though I be utterly unworthy of it.” They that think they are fit for mercy, will never get it, nor indeed can ask it. But they that think they are needy of it, and that it is fit for them, will both ask it and get it.
Source: http://www.puritanboard.com/showthread.php/90834-Mercy-is-fit-for-me-exactly, Comment 1