‘And Cain talked with Abel his brother: and it came to pass, when they were in the field, that Cain rose up against Abel his brother, and slew him.’ Genesis 4:8
SUGGESTED FURTHER READING: 1 Samuel 18:1–30
Observe the progress of sin: Cain first indulged anger and then proceeded to murder. One is the seed, the other the fruit. Therefore, whoever hateth his brother is a murderer in the sight of God [Matthew 5:21–22]—if he was not restrained by his providence he would proceed to the outward act. Take heed of indulging dislike and ill will—it may lead you farther than you are aware, to do injury, if not to touch the life. However, the law of God will condemn you, even for evil thoughts.
Note the nature of a religious profession and what it will expose you to: look through the whole Bible—you may trace the same spirit. Isaac, the child of the promise, was mocked by Ishmael. This the Apostle calls persecution [Galatians 4:29]. The life of Jacob was sought by Esau because God gave him the blessing. So David was hunted like a partridge upon the mountains. Christ and his apostles were despised and opposed even to the death. Marvel not if the world hate you. And see the necessity of a continual dependence upon grace, that you may not fear them who can kill the body but can do no more. For if you are strengthened by faith in him who is invisible, you will dare to obey God rather than man.
What we owe to the providence and goodness of God in restraining the wrath of man! The same spirit is always awake, but he who rules the stormy wind and the raging waves of the sea, keeps it within bounds. Especially in our land and day, we have reason to be thankful.
FOR MEDITATION: If therefore you meet with some unkind reflections and misrepresentations from men of unfeeling and mercenary spirits, you will bear it patiently when you think of him who endured the contradiction of sinners against himself.
John Newton to William Wilberforce, 4 August 
[during the struggle to abolish the slave trade]
SERMON SERIES: GENESIS, NO. 12 [2/4], GENESIS 4:8
John Newton and Marylynn Rouse, 365 Days with Newton (Leominster, UK: Day One Publications, 2006), 198.