And this is the testimony: God has given us eternal life, and this life is in his Son. Whoever has the Son has life; whoever does not have the Son of God does not have life. I write these things to you who believe in the name of the Son of God so that you may know that you have eternal life. (1 John 5:11-13 NIV)
Why does John write this letter to the church? He makes his purpose clear in this passage. He writes so that those who have believed in the name of Christ might have confidence in their salvation; that they can have an assurance of eternal life. I have known many who struggled with this assurance. And I know others who believe you cannot know for sure until you stand before God. But that is not the message of John here. He says we can know now.
How can you have an assurance of eternal life? John makes it clear in this passage. Whoever has the Son has life. Whoever does not have the Son does not have life. How do we have the Son? By believing in him. But this belief is more than mental assent. It is placing your trust, your life, in him. It is making him Lord in your own life. If Jesus is Lord in your life, then you have the Son. And you can know that you have eternal life. It is not a guessing game. We don’t have to hope that we have eternal life. We can know.