Charles H. Spurgeon on Psalms 51:13

Then will I teach transgressors thy ways. It was his fixed resolve to be a teacher of others; and assuredly none instruct others so well as those who have been experimentally taught of God themselves. Reclaimed poachers make the best gamekeepers. Huntingdon's degree of S.S., or Sinner Saved, is more needful for a soul winning evangelist than either M.A. or D.D. The pardoned sinner's matter will be good, for he has been taught in the school of experience, and his manner will be telling, for he will speak sympathetically, as one who has felt what he declares. The audience the psalmist would choose is memorable —he would instruct transgressors like himself; others might despise them, but, "a fellow feeling makes us wondrous kind." If unworthy to edify saints, he would creep in along with the sinners, and humbly tell them of divine love. The mercy of God to one is an illustration of his usual procedure, so that our own case helps us to understand his "ways, "or his general modes of action: perhaps, too, David under that term refers to the preceptive part of the word of God, which, having broken, and having suffered thereby, he felt that he could vindicate and urge upon the reverence of other offenders. And sinners shall be converted unto thee. My fall shall be the restoration of others. Thou wilt bless my pathetic testimony to the recovery of many who, like myself, have turned aside unto crooked ways. Doubtless this Psalm and the whole story of David, have produced for many ages the most salutary results in the conversion of transgressors, and so evil has been overruled for good.