But I already believe that Jesus is God, that He lived a sinless life, and that He died and rose again.
God says…
Jesus said to her [Martha], "I am the resurrection and the life. He who believes in Me, though he may die, he shall live. And whoever lives and believes in Me shall never die. Do you believe this?" She said to Him, "Yes, Lord, I believe that You are the Christ, the Son of God, who is to come into the world."
The Gospel of John
Chapter 11, Verses 25-27
That means…
Just believing in Jesus’ deity, sinlessness, death, and resurrection won’t give you assurance that you have eternal life. Millions of people believe those things and yet lack assurance. The reason is because it is sadly possible to believe that Jesus died and rose again, and yet not believe His promise to give eternal life freely to all who believe in Him. Multitudes of people believe that Jesus’ death and resurrection was necessary for their salvation, but that it wasn’t enough. They believe that their commitment, obedience, and good works are also necessary for them to go to heaven.
To be sure you are saved, you must believe that Jesus Christ has given you eternal life as He said He would if you believed in Him. It’s simply a matter of taking God at His word. Martha did, and she knew she had eternal life. So can you.