The law of the Lord is perfect, the psalmist says, converting the soul. For the one who receives the word of God in faith, the law teaches us to stay away from the precipice of sin, apostasy, and damnation. The law of God makes the simple wise.
Hear then, this warning from the law. The warning is for all God’s people, and describes how the long, deceitful slide into sin happens.
“Who can understand his errors?” (Ps. 19:12). David asks. He then outlines the growth and progress of the central confusion. He says first “cleanse thou me from secret faults” (v. 12). Then he asks God to keep him back from presumptuous sins (v. 13). As a result, protected from secret sin and from presumptuous sin, he will be protected from “the great transgression” (v. 13).
So there it is—a diagram of the long slide into darkness. Secret sin, presumptuous sin, and the great transgression. When the great transgression occurs, scandalizing everyone, whether it is embezzlement, desertion of a spouse, denial of the faith, we must never assume that this great transgression sprang into existence from nothing. This is not a thunderhead that just appeared—there was a weather pattern that preceded it, and which necessitated it.
Secret sin is indulged in the recesses of heart or mind. Secret sin occurs away from others, while alone on the computer, or while alone on a business trip.
Presumptuous sin is more open, and usually involves a circle of complicit friends—people who will let you slide because they want you to let them slide. All forms of piety are mocked as over-scrupulous. Cutting corners becomes socially expected and even approved.
And many Christians think to deny the Word of God, and just keep it right there. Secret sin need never get out, and presumptuous sins will just stay put, remaining within the compromised boundaries established for them. But that is like being a little bit pregnant.
The only way to avoid the great transgression is to repent—repent of the secret sins, and repent of any circle of friends that helps to presume upon the kindness and forbearance of God.