The Puritans (and their admirers, past and present) actually maintained that only one who has come thoroughly to hate sin can turn wholeheartedly from it to Christ. Contrition is necessitated not by the terms of the gospel, which calls us to Christ directly, but by the state of the fallen human heart. God uses the law to pave the way for the gospel by making us see not only our guilt but also the ugliness, nastiness, and repulsiveness of our previous ways, so that we cease to love them; and that sets us free to love Christ when he calls us to follow him into different ways.
The alternative is a false conversion that is illustrated by seed falling on stony ground in Jesus’s parable of the soils. Today we see people who have been pressured to make decisions, who received the word of pardon and peace with joy, and who promise to follow Christ henceforth, but then find the old way of Christlessness and sin more attractive than the new way of resisting sin out of loyalty to Christ and suffering in consequence (see Heb. 12:3-4). So they go rapidly back to their old ways. That shows such inner conviction and change as was experienced never went deep enough to make the life of sin intolerable forever after, or to produce clear understanding that Christ will only save us from sin, never in sin. If we are to avoid producing false conversions, we must make much of the law, sin, and repentance in our communication, and not press people for gestures of decision until we have done all we can to make sin hateful in their eyes and have reason to judge that they have received this part of the message. But this deep conviction of sin, like the conviction that the gospel announces realities that impinge on life, comes only from the Holy Spirit’s application of the word we communicate.
– David Wells, Turning to God, pp. 87-88