Article 5: The Inadequacy of the Law
In this respect, what is true of the light of nature is true also of the Ten Commandments given by God through Moses specifically to the Jews. For man cannot obtain saving grace through the Decalogue, because, although it does expose the magnitude of his sin and increasingly convict him of his guilt, yet it does not offer a remedy or enable him to escape from his misery, and, indeed, weakened as it is by the flesh, leaves the offender under the curse.
Article 6: The Saving Power of the Gospel
What, therefore, neither the light of nature nor the law can do, God accomplishes by the power of the Holy Spirit, through the Word or the ministry of reconciliation. This is the gospel about the Messiah, through which it has pleased God to save believers, in both the Old and the New Testament.
(The Canons of Dort, The Third and Fourth Main Points of Doctrine, Human Corruption, Conversion to God, and the Way It Occurs, Articles 5-6)