New City CatechismSýnishorn

Question: Can anyone keep the law of God perfectly?

Answer: Since the fall, no mere human has been able to keep the law of God perfectly, but consistently breaks it in thought, word, and deed.

Commentary: As a traveller, in his way meeting with a violent storm of thunder and rain, immediately turns out of his way to some house or tree for his shelter; but yet this causeth him not to give over his journey; so soon as the storm is over he returns to his way and progress again. So it is with men in bondage to sin: the law meets with them in a storm of thunder and lightning from heaven, terrifies and hinders them in their way; this turns them for a season out of their course; they will run to prayer or amendment of life, for some shelter from the storm of wrath which is feared coming upon their consciences. But is their course stopped? are their principles altered?

Not at all; so soon as the storm is over…they return to their former course, in the service of sin again. Never let us reckon that our work in contending against sin, in crucifying, mortifying, and subduing of it, is at an end. The place of its habitation is unsearchable; and when we may think that we have thoroughly won the field, there is still some reserve remaining that we saw not, that we knew not of. Many conquerors have been ruined by their carelessness after a victory; and many have been spiritually wounded after great successes against this enemy…. There is no way for us to pursue sin in its unsearchable habitation but by being endless in our pursuit.