1 John 5:10-13
10 The one who believes in the Son of God has the testimony in himself; the one who does not believe God has made Him a liar because he has not believed in the testimony that God has given concerning His Son. 11 And the testimony is this, that God has given us eternal life, and this life is in His Son. 12 He who has the Son has the life; he who does not have the Son of God does not have the life. 13 These things I have written to you who believe in the name of the Son of God, so that you may know that you have eternal life.
God wants you to be secure in your relationship with Him, and He wants you to feel secure. He does several things to make your security a reality. First, when you believed in Jesus, He put the testimony He has given within you. This is also called “the witness of the Spirit” You can read about it in Romans 8 which explains how the Holy Spirit talks to your spirit assuring you that you’re OK.
What He communicates is that in Jesus God has given you eternal life. If you don’t have the Son, you don’t have life, but everyone who has the Son by faith has the life. He doesn’t speak audibly to you, but a feeling of joy, warmth, calm, and peace comes up in your chest and you can tell He is talking with you. This most often happens while you are reading your Bible and praying. That’s why John says he wrote his letters to Christians so they may know they have eternal life.
How do you get the testimony? By believing in Jesus. Did you do anything to earn your eternal life? No, you received it by faith. Can you lose it? No, it’s eternal, nothing can take it away from you. You couldn’t earn it, you can’t be canceled. Read John 10:27-30 and find out how you could possibly lose your eternal life.
When the devil comes around lying to you about losing anything, remind him about what he lost when he rebelled against God. Tell him how Jesus took your place on the Cross and paid for every sin forevermore and nothing can change that. Then go back and re-read the I gave you. In fact, memorize Romans 8 and be ready for the enemy’s attack.