This is an excerpt from Nehemiah Coxe’s A Discourse of the Covenants, first published in 1681, and reprinted as the first part of Covenant Theology: From Adam to Christ (Palmdale: Reformed Baptist Academic Press, 2005), 33-34.
The great interest of man’s present peace and eternal happiness is most closely concerned in religion. And all true religion since the fall of man must be taught by divine revelation which God by diverse parts and after a diverse manner has given out to his church.He caused this light gradually to increase until the whole mystery of his grace was perfectly revealed in and by Jesus Christ in whom are hid all the treasures of wisdom and knowledge. God, whose works were all known by him from the beginning, has in all ages disposed and ordered the revelation of his will to men, his transactions with them, and all the works of his holy providence toward them, with reference to the fullness of time, and the gathering of all things to a head in Christ Jesus. So in all our search after the mind of God in the holy Scriptures we are to manage our inquiries with reference to Christ. Therefore the best interpreter of the Old Testament is the Holy Spirit speaking to us in the New. There we have the clearest light of the knowledge of the glory of God shining on us in the face of Jesus Christ, by unveiling those counsels of love and grace that were hidden from former ages and generations.
Nevertheless the greater light of the New Testament does in no way abate the usefulness of the Old; rather it obliges us all the more to a humble and diligent study of it. This is (as for so many reasons, so also for this one) because the mystery of the gospel cannot be thoroughly apprehended by us without some good understanding of the economy of the law and also of the state of things before the law. The mutual respect and dependence of the Old and New Testaments are such that neither can be understood apart or without the other, nor can an entire system of truth as it is in Jesus be collected except from both.