Sin

  "Through one man sin entered into the world and death through sin, and so death spread to all men because they had all sinned." —Romans 5:12

Sin is any action, feeling, or thought that goes against God’s standards. It includes breaking God’s laws by doing what is wrong, or unrighteous, in God’s sight (1 John 3:4; 5:17).

From the beginning
1 John 3:8 "The one who practices sin originates with the Devil, because For this purpose the Son of God was made manifest, to break up the works of the Devil."

Mastery over sin
Then Jehovah said to Cain: “Why are you so angry and dejected? If you turn to doing good, will you not be restored to favor? But if you do not turn to doing good, sin is crouching at the door, and its craving is to dominate you; but will you get the mastery over it?” — Genesis 4:6,7. God gave this warning when it was apparent that Cain was on a very dangerous course. Cain, however, did not heed God's warning, and thus he suffered for it (Gen. 4:11-13).

The hardened heart
"Do not harden your hearts as on the occasion of provoking to bitter anger, as in the day of testing in the wilderness, where your forefathers put me to the test and tried me, despite seeing my works for 40 years. This is why I became disgusted with this generation and said: ‘They always go astray in their hearts, and they have not come to know my ways.’ So I swore in my anger: ‘They will not enter into my rest.’” Beware, brothers, for fear there should ever develop in any one of you a wicked heart lacking faith by drawing away from the living God." — Heb 3:8-12

"Let us therefore do our utmost to enter into that rest, so that no one may fall into the same pattern of disobedience. For the word of God is alive and exerts power and is sharper than any two-edged sword and pierces even to the dividing of soul and spirit, and of joints from the marrow, and is able to discern thoughts and intentions of the heart. And there is not a creation that is hidden from his sight, but all things are naked and openly exposed to the eyes of the one to whom we must give an account." — Heb 4:11-13

"So keep strict watch that how you walk is not as unwise but as wise persons, making the best use of your time, because the days are wicked." — Eph 5:15-17.

Death
The sting producing death is sin, and the power for sin is the Law." — 1 Cor 15:56