That first petition conceives of the divine dealing with sin as being the erasure of a writing, perhaps of an indictment. There is a special significance in the use of the word here, because it is also employed in the description of the Levitical ceremonial of the ordeal, where a curse was written on a scroll and blotted out by the priest. But apart from that the metaphor is a natural and suggestive one. Our sin stands written against us. The long gloomy indictment has been penned by our own hands. Our past is a blurred manuscript, full of false things and bad things. We have to spread the writing before God, and ask Him to remove the stained characters from its surface, that once was fair and unsoiled.
Ah, brethren! some people tell us that the past is irrevocable, that the thing once done can never be undone, that the life's diary written by our own hands can never be cancelled. The melancholy theory of some thinkers and teachers is summed up in the words, infinitely sad and despairing when so used, 'What I have written I have written.' Thank God! we know better than that. We know who blots out the handwriting 'that is against us, nailing it to His Cross.' We know that of God's great mercy our future may 'copy fair our past,' and the past may be all obliterated and removed. And as sometimes you will find in an old monkish library the fair vellum that once bore lascivious stories of ancient heathens and pagan deities turned into the manuscript in which a saint has penned his Contemplations, an Augustine his Confessions, or a Jerome his Translations, so our souls may become palimpsests. The old wicked heathen characters that we have traced there may be blotted out, and covered over by the writing of that divine Spirit who has said, 'I will put My laws into their minds, and write them in their hearts.' As you run your pen through the finished pages of your last year's diaries, as you seal them up and pack them away, and begin a new page in a clean book on the first of January, so it is possible for every one of us to do with our lives. Notwithstanding all the influence of habit, notwithstanding all the obstinacy of long-indulged modes of thought and action, notwithstanding all the depressing effect of frequent attempts and frequent failures, we may break ourselves off from all that is sinful in our past lives, and begin afresh, saying, 'God helping me! I will write another sort of biography for myself for the days that are to come.'
We cannot erase these sad records from our past. The ink is indelible; and besides all that we have visibly written in these terrible autobiographies of ours, there is much that has sunk into the page, there is many a 'secret fault,' the record of which will need the fire of that last day to make it legible, Alas for those who learn the black story of their own lives for the first time then! Learn it now, my brother! and learn likewise that Christ can wipe it all clean off the page, clean out of your nature, clean out of God's book. Cry to Him, with the Psalmist, 'Blot out my transgressions!' and He will calm and bless you with the ancient answer, 'I have blotted out as a thick cloud thy transgressions, and as a cloud thy sins.'
Then there is another idea in the second of these prayers for forgiveness: '_Wash me throughly_ from mine iniquity.' That phrase does not need any explanation, except that the word expresses the antique way of cleansing garments by treading and beating. David, then, here uses the familiar symbol of a robe, to express the 'habit' of the soul, or, as we say, the character. That robe is all splashed and stained. He cries to God to make it a robe of righteousness and a garment of purity.