His main idea in this sermon was that in every sense in which death reigned and ruled over God's people, they are now completely delivered. Newton wasn't suggesting that the followers of Christ would no longer experience the ramifications of sin, but rather that death has been defeated by Christ and the one day all those in christ would be free forever from death's power.
One of his main points relates to the tyranny of Satan. Newton proclaims, "One branch of the death due to sin, is the tyranny and power of Satan." Satan's tyranny, says Newton, is connected to the reign of death. Newton goes on from there to preach a compelling description of Christ's work reversing the tyranny of Satan through his victory over death. This excerpt is the reason for this post; I had to share it. Enjoy, and be edified.
One branch of the death due to sin, is the tyranny and power of Satan. For a time he ruled in their hearts, as in his own stronghold; and while they were blinded by his influence, they were little affected with their bondage. Hard as his service was, they did not often complain of it. They were lead by him according to his will, for the most part without resistance; or, if they attempted to resist, they found it was in vain. But in His own hour, their Lord who had bought them, dispossessed their strong enemy and claimed their hearts for Himself. Yet after they were thus set free from his [Satan’s] ruling power, this adversary was always plotting and fighting against them. How much have some of them suffered from his subtle wiles, and his fiery darts! from his rage as a roaring lion, from his cunning as a serpent lying in their path, and from his attempts to deceive them under the semblance of an angel of light (II Corinthians 11:14)! But now they are placed out of his reach. Death and Satan are swallowed up. The victory is complete. The wicked one shall never have access to touch or disturb them anymore. Now he is shut up in his own place, and the door sealed, no more to open. While he was permitted to vex and worry them, he acted under a limited commission which he could not exceed; all was directed and overruled by the wisdom and love of their Lord, for their advantage. Such exercises were necessary then, to discover to them more of the weakness and vileness of their own hearts, to make them more sensible of their dependence upon their Saviour, and to afford them affecting proofs of His power and care engaged in their behalf. But they are necessary no longer. Their warfare is finished. They are now where the wicked cease from troubling, and where the weary are at rest (Job 3:17).