Whole chapter discussed by Augustine of Hippo —
Overcoming the World
1Everyone who believes that Jesus is the Christ has been born of God, and everyone who loves the Father also loves those born of Him. 2By this we know that we love the children of God: when we love God and keep His commandments. 3For this is the love of God, that we keep His commandments. And His commandments are not burdensome, 4because everyone born of God overcomes the world. And this is the victory that has overcome the world: our faith.
5Who then overcomes the world? Only he who believes that Jesus is the Son of God. 6This is the One who came by water and blood, Jesus Christ—not by water alone, but by water and blood. And it is the Spirit who testifies to this, because the Spirit is the truth. 7For there are three that testify: 8the Spirit, the water, and the blood—and these three are in agreement.
God’s Testimony about His Son
9Even if we accept human testimony, the testimony of God is greater. For this is the testimony that God has given about His Son. 10Whoever believes in the Son of God has this testimony within him; whoever does not believe God has made Him out to be a liar, because he has not believed in the testimony that God has given about His Son.
11And this is that testimony: God has given us eternal life, and this life is in His Son. 12Whoever has the Son has life; whoever does not have the Son of God does not have life.
Effective Prayer
13I have written these things to you who believe in the name of the Son of God, so that you may know that you have eternal life. 14And this is the confidence that we have before Him: If we ask anything according to His will, He hears us. 15And if we know that He hears us in whatever we ask, we know that we already possess what we have asked of Him.
16If anyone sees his brother committing a sin not leading to death, he should ask God, who will give life to those who commit this kind of sin. There is a sin that leads to death; I am not saying he should ask regarding that sin. 17All unrighteousness is sin, yet there is sin that does not lead to death.
The True God
18We know that anyone born of God does not keep on sinning; the One who was born of God protects him, and the evil one cannot touch him. 19We know that we are of God, and that the whole world is under the power of the evil one. 20And 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.
21Little children, keep yourselves from idols.