Neonomianism (Greek lit. new law) in Christian theology is the doctrine that the Gospel is a new law the requirements of which we fulfill by faith and repentance, most often associated with the theology of Richard Baxter (1615-1691).
Richard Baxter defended this view when he wrote, "In our first Believing we take Christ in the Relations of a Saviour, and Teacher, and Lord, to save us from all sin, and to lead us to glory. This therefore importeth that we accordingly submit unto him, in those his Relations, as a necessary means to the obtaining of the benefits of the Relations. Our first faith is our Contract with Christ….And all Contracts of such nature, do impose a necessity of performing what we consent to and promise, in order to the benefits….Covenant-making may admit you, but its the Covenant-keeping that must continue you in your privileges." (Richard Baxter, Aphorisms of Justification)
William Styles defines neonomianism as, "A schemed of Divinity propounded by Daniel Williams, D.D., which held that God has receded from the demands of the Moral Law, and given up its original obligations—and that the Gospel is a New Law, but of milder requirements, in which Faith, Repentance, and sincere though imperfect Obedience, are substituted in the room of the perfect and perpetual Obedience required by the original Law." (William Styles, A Manual of Faith and Practice)
Isaac Chauncy (1632-1712) is one of the leading opponents of neonomianism. He sets forth his arguments against Daniel Williams in his book, Neonomianism Unmask'd.