Old typewriters had a backspace button, but it wasn’t like the one on your computer today. On the typewriter, the backspace simply moved the carriage back one space, to the character previously typed, but all you could do was overtype that character (leaving an ugly mark) or grab the whiteout bottle (leaving an obvious spot of correction). 
As word processors came along, the backspace function changed, and now on your computer (and on your mobile device), you can backspace all you want, which deletes everything previously typed.
Long before typewriters were ever invented, God had a backspace button. It didn’t leave an ugly mark. And, when applied by God, there isn’t even a noticeable spot of correction. When a Christian repents, he is backing his carriage up, acknowledging wrong and asking God to forgive (i.e., erase) the sinful mistake and all guilt associated with it. And when God erases, He thoroughly “cleanses from all sin” (1 John 1:7, 9). Thank God for His backspace button! Use it often!