Why is Cain angry?

He is angry enough that he is going to slay his brother. Back of premeditated murder there always is anger.

Our Lord said that, if you are angry with your brother without a cause, you are guilty of murder.
Back of anger is jealousy, and back of jealousy is pride. There is no sense of sin whatsoever in spiritual pride.

James put it in language like this: “Then when lust hath conceived, it bringeth forth sin: and sin, when it is finished, bringeth forth death” (James 1:15).

Cain’s anger led to murder, but back of that was his jealousy and also his pride.
And that is how God deals with him.

He says to Cain, “If thou doest well, shalt thou not be accepted?”

Actually, the meaning is better translated as, “Shalt thou not have excellency?”

The eldest son always occupied a place of preeminence, and this boy thinks that now he will lose that. God tells him there is no reason for him to lose it if he does well. To do well would be to bring that which God had accepted from Abel, a sacrifice and the acknowledgment that he was a sinner.
But not this boy—he’s just angry.

“Sin lieth at the door.”

There are those who have interpreted this as meaning that a sin offering lies at the door; that is, that there is the little lamb lying at the door. That makes sense because that was true, but I do not think it means the sin offering here.

Up to this time and beyond this time, in fact, up until Moses, as far as I can tell from the Word of God, there was no sin offering. You find the instructions given for the sin offering in the Book of Leviticus. In the first part of that book, five offerings are given, and one is the sin offering.

The sin offering did not come into existence until the law was given. That is the thing that Paul is saying in Romans 3:20: “. . . For by the law is the knowledge of sin.”

The offerings that were brought up to that time were burnt offerings.

Job in his day, which obviously was before Moses, brought a burnt offering. It was not in any way a sin offering. I think if you will examine the Scriptures, you will find that that is true.

It is obvious that Cain did not realize how vulnerable to sin he was. When God said to him that “sin lieth at the door,” I believe He was saying that sin, like a wild beast, was crouching at the door waiting to pounce on him the moment he stepped out.

For that reason Cain needed a sacrifice that would be acceptable to God for sin, a sacrifice that pointed to Christ.

“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” (1 John 3:12).

“If thou doest not well, sin lieth at the door.”

To do well would have been to bring the kind of offering that Abel had brought, a burnt offering.
You find that Abraham also offered a burnt offering, for there could be no transgression until the law was given; that is, sin would not become a trespass against law until then. Therefore, you find that God actually protected this man Cain.

Our Scripture Of The Week Is:

Proverbs 15:1-2 KJV
[1] A soft answer turneth away wrath: but grievous words stir up anger.
[2] The tongue of the wise useth knowledge aright: but the mouth of fools poureth out foolishness.

Solomon offers wise advice about how to respond to anger. He says a soft or gentle answer can defuse a potentially explosive situation.

The word translated "wrath" here means rage. This is the kind of volatile anger that eventually leads to physical conflict. When we're insulted or angry, the easiest course of action is to become furious and respond to the other person's rage with similar rage.

However, if a person chooses to respond to rage with harsh, hurtful words, he will make matters worse. Cutting, bitter responses only cause the enraged person's anger to escalate; that results in further hostility.

In contrast, a cool temper refuses to fight fire with fire. The wise person answers gently, and that gentleness extinguishes the fire. At the very least, it gives no more fuel for it to burn. A calm, polite response can take a great deal of tension out of an argument.

This response calls for wisdom, thoughtfulness, concern for the other person, and self-discipline.

Romans 12:19–20 tells us not to avenge ourselves, but to know the Lord will repay the wrong. The believer's responsibility is to show kindness to an enemy:

"Do not be overcome by evil, but overcome evil with good" (Romans 12:21).

Addressing the subject of speech in this verse, Solomon observes that the wise person compliments knowledge by speaking wisely. Wise speech persuades others to pursue and gain knowledge.

Likewise, the thoughtful person is focused on concepts such as truth and wisdom, rather than merely filling the air with words.

The fool, however, speaks foolishly. Words gush out of their mouths thoughtlessly and reveal a lack of knowledge. Critics of Christian faith often rely on volume—both in the sense of bulk and noise—instead of reason. Through a flood of repeated criticisms, angry words, and shallow attacks, they seek to avoid deeper engagement on subjects.

Jesus, who possessed all the treasures of wisdom and knowledge (Colossians 2:3), astounded people with His wise words. Even at the age of twelve Jesus manifested wisdom when He conversed with the teachers in the temple.

Luke 2:47 reports that "all who heard him were amazed at his understanding and his answers."

In the synagogue in Nazareth, Jesus' hometown, Jesus taught those who were present. Subsequently, those who heard Him, "were astonished, and said, 'Where did this man get this wisdom and these mighty works?'" (Matthew 13:54).

Christ also taught His disciples to pray wisely instead of using empty words. He said, "When you pray, do not heap up empty phrases as the Gentiles do, for they think that they will be heard for their many words. Do not be like them, for your Father knows what you need before you ask him" (Matthew 6:7–8).