According to His promise as recorded in Revelation 3:20, where is Christ right now in relation to you? Christ said that He would come into your life and be your Savior and friend so you can know Him personally. Would He mislead you? On what authority do you know that God has answered your prayer? (The trustworthiness of God Himself and His Word.)
The Bible promises eternal life to all who receive Christ.
“And this is the testimony: God has given us eternal life, and this life is in His Son. He who has the Son has life; he who 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)
Thank God often that Christ is in your life and that He will never leave you (Hebrews 13:5). You can know on the basis of His promise that Christ lives in you and that you have eternal life from the very moment you invite Him in.