Heb 11:6, 1 Jn 3:12, 1 Pt 5:8, Jn 8:34,44, Jude 1:11
Cain did not believe and did not wait for the Christ he had heard from his father Adam. As a result, he became a slave to sin. (Genesis 4:7-8, 1 John 3:12, Jude 1:11, John 8:34, 44)
Genesis 4:7 If thou doest well, shalt thou not be accepted? and if thou doest not well, sin lieth at the door. And unto thee shall be his desire, and thou shalt rule over him. 8 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.
1 John 3:12 Not as Cain, who was of that wicked one, and slew his brother. And wherefore slew he him? Because his own works were evil, and his brother's righteous.
Jude 1:11 Woe unto them! for they have gone in the way of Cain, and ran greedily after the error of Balaam for reward, and perished in the gainsaying of Core.
John 8:34 Jesus answered them, Verily, verily, I say unto you, Whosoever committeth sin is the servant of sin. 44 Ye are of your father the devil, and the lusts of your father ye will do. He was a murderer from the beginning, and abode not in the truth, because there is no truth in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it.
We should be sober and watchful, trusting in Christ and waiting for Christ. (1 Peter 5:8, Hebrews 11:6)
1 Peter 5:8 Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour:
Hebrews 11:6 But without faith it is impossible to please him: for he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him.