John, him who wrote the Gospel of John and Revelations, wrote 3 epistles. Along with Jude and Rev, these form the last 5 books of The Bible.
1 John 1:
Walking in the light
5This is the message we have heard from him and declare to you: God is light; in him there is no darkness at all.
6If we claim to have fellowship with him yet walk in the darkness, we lie and do not live by the truth.
7But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus, his Son, purifies us from all sin.
8If we claim to be without sin, we deceive ourselves and the truth is not in us.
10If we claim we have not sinned, we make him out to be a liar and his word has no place in our lives.
1 John 2:
4The man who says, "I know him," but does not do what he commands is a liar, and the truth is not in him.
This refers to Cain:
9Anyone who claims to be in the light but hates his brother is still in the darkness.
10Whoever loves his brother lives in the light, and there is nothing in him to make him stumble.
11But whoever hates his brother is in the darkness and walks around in the darkness; he does not know where he is going, because the darkness has blinded him.
Do Not Love the World
15Do not love the world or anything in the world. If anyone loves the world, the love of the Father is not in him.
16For everything in the world—the cravings of sinful man, the lust of his eyes and the boasting of what he has and does—comes not from the Father but from the world.
17The world and its desires pass away, but the man who does the will of God lives forever.
Warning Against Antichrists
18Dear children, this is the last hour; and as you have heard that the antichrist is coming, even now many antichrists have come. This is how we know it is the last hour.
19They went out from us, but they did not really belong to us. For if they had belonged to us, they would have remained with us; but their going showed that none of them belonged to us.
22Who is the liar? It is the man who denies that Jesus is the Christ. Such a man is the antichrist—he denies the Father and the Son.
1 John 3:
4Everyone who sins breaks the law; in fact, sin is lawlessness.
6No one who lives in him keeps on sinning. No one who continues to sin has either seen him or known him.
8He who does what is sinful is of the devil, because the devil has been sinning from the beginning. The reason the Son of God appeared was to destroy the devil's work.
10This is how we know who the children of God are and who the children of the devil are: Anyone who does not do what is right is not a child of God; nor is anyone who does not love his brother.
Love one another
11This is the message you heard from the beginning: We should love one another.
12Do not be like Cain, who belonged to the evil one and murdered his brother. And why did he murder him? Because his own actions were evil and his brother's were righteous.
13Do not be surprised, my brothers, if the world hates you.
14We know that we have passed from death to life, because we love our brothers. Anyone who does not love remains in death.
15Anyone who hates his brother is a murderer, and you know that no murderer has eternal life in him.
16This is how we know what love is: Jesus Christ laid down his life for us. And we ought to lay down our lives for our brothers.
17If anyone has material possessions and sees his brother in need but has no pity on him, how can the love of God be in him?
This can apply to God or Satan, whichever you choose to serve:
22and receive from him anything we ask, because we obey his commands and do what pleases him.
. 24Those who obey his commands live in him, and he in them. And this is how we know that he lives in us: We know it by the Spirit he gave us.
1 John 4:
Test the Spirits
1Dear friends, do not believe every spirit, but test the spirits to see whether they are from God, because many false prophets have gone out into the world.
2This is how you can recognize the Spirit of God: Every spirit that acknowledges that Jesus Christ has come in the flesh is from God,
3but every spirit that does not acknowledge Jesus is not from God. This is the spirit of the antichrist, which you have heard is coming and even now is already in the world.
This regards the two beasts from Rev 13:
5They are from the world and therefore speak from the viewpoint of the world, and the world listens to them.
6We are from God, and whoever knows God listens to us; but whoever is not from God does not listen to us. This is how we recognize the Spirit[a] of truth and the spirit of falsehood.
8Whoever does not love does not know God, because God is love.
18There is no fear in love. But perfect love drives out fear, because fear has to do with punishment. The one who fears is not made perfect in love.
20If anyone says, "I love God," yet hates his brother, he is a liar. For anyone who does not love his brother, whom he has seen, cannot love God, whom he has not seen.
21And he has given us this command: Whoever loves God must also love his brother.
1 John 5:
4for everyone born of God overcomes the world. This is the victory that has overcome the world, even our faith.
15And if we know that he hears us—whatever we ask—we know that we have what we asked of him.
Cain again:
16If anyone sees his brother commit a sin that does not lead to death, he should pray and God will give him life. I refer to those whose sin does not lead to death. There is a sin that leads to death. I am not saying that he should pray about that.
The world is under the control of Satan:
19We know that we are children of God, and that the whole world is under the control of the evil one.
2 John:
7Many deceivers, who do not acknowledge Jesus Christ as coming in the flesh, have gone out into the world. Any such person is the deceiver and the antichrist.
11Anyone who welcomes him shares in his wicked work.
3 John:
11Dear friend, do not imitate what is evil but what is good. Anyone who does what is good is from God. Anyone who does what is evil has not seen God.