There is no way of coming to that knowledge of sin, which is necessary to repentance, and therefore to peace and pardon, but by trying our hearts and lives by the law. In his own case the apostle would not have known the sinfulness of his thoughts, motives, and actions, but by the law.
That perfect standard showed how wrong his heart and life were, proving his sins to be more numerous than he had before thought, but it did not contain any provision of mercy or grace for his relief.
He is ignorant of human nature and the perverseness of his own heart, who does not perceive in himself a readiness to fancy there is something desirable in what is out of reach. We may perceive this in our children, though self-love makes us blind to it in ourselves.
The more humble and spiritual any Christian is, the more clearly will he perceive that the apostle describes the true believer, from his first convictions of sin to his greatest progress in grace, during this present imperfect state.
St. Paul was once a Pharisee, ignorant of the spirituality of the law, having some correctness of character, without knowing his inward depravity. When the commandment came to his conscience by the convictions of the Holy Spirit, and he saw what it demanded, he found his sinful mind rise against it.
He felt at the same time the evil of sin, his own sinful state, that he was unable to fulfil the law, and was like a criminal when condemned. But though the evil principle in the human heart produces sinful motions, and the more by taking occasion of the commandment; yet the law is holy, and the commandment holy, just, and good.
It is not favourable to sin, which it pursues into the heart, and discovers and reproves in the inward motions thereof. Nothing is so good but a corrupt and vicious nature will pervert it. The same heat that softens wax, hardens clay.
Food or medicine when taken wrong, may cause death, though its nature is to nourish or to heal. The law may cause death through man's depravity, but sin is the poison that brings death. Not the law, but sin discovered by the law, was made death to the apostle.
The ruinous nature of sin, and the sinfulness of the human heart, are here clearly shown.