The apostle John finished his first letter with three things that we know in Jesus Christ:
First, “We know that everyone who has been born of God does not keep on sinning, but he who was born of God protects him, and the evil one does not touch him” (1 John 5:18). If we have become a Christian then we have repented of our sins and have promised God that we’re not going to sin anymore. That doesn’t mean that it is impossible for us to sin. We can still sin if we so choose. But if our hearts are right with God and we are striving to live for Him then we are going to be diligent not to sin. God will help us overcome evil. He can protect us from the evil one.
Secondly, “We know that we are from God, and the whole world lies in the power of the evil one” (1 John 5:19). The god of this world, the evil one is Satan. Satan has corrupted this world with sin. He is the father of sin. But God through Christ has freed us from sin and death. The Lord of heaven has delivered us from the power of the evil one. We are of God now. The rest of the world may still be serving the devil but we are serving the Lord Jesus Christ. We need to be praying for those who are still lost to come to their senses, repent, and obey the Gospel. Give their lives to God.
Finally, John says that “we know that the Son of God has come and has given us understanding, so that we may know Him who is true; and we are in Him who is true, in His son Jesus Christ. He is the true God and eternal life” (1 John 5:20). Jesus, the Son of God came to this earth to bring us the good news of salvation. The knowledge and understanding we needed to know God. His righteousness. His love. His wrath. His grace through Jesus Christ. He is the true God. He has given us eternal life.
Because we know all of this we can know that we have eternal life (1 John 5:13). Stay away from sin. Be an obedient child of God. Be holy as He is holy. Don’t follow the lies of Satan. Come out of worldliness. Understand what the will of the Lord is and what is pleasing to Him. Then live it. Be righteous. Be God’s. Have eternal life.