You mean I really can be sure?
God says…
If we receive the witness of men, the witness of God is greater; for this is the witness of God which He has testified of His Son. He who believes in the Son of God has the witness in himself; he who does not believe God has made Him a liar, because he has not believed the testimony that God has given of His Son. And this is the testimony: that 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 does not have life. These things I have written to you who believe in the name of the Son of God, that you may know that you have eternal life, and that you may continue to believe in the name of the Son of God.
The First Letter of John
Chapter 5, Verses 9-13
That means…
Yes, you can really know that you have eternal life. God didn’t say that you could guess or hope or think that you have eternal life. He said you could know.
In fact, if you don’t know that you’re saved, then you aren’t focusing on the truth of God’s testimony. All you need to do to be sure you have eternal life is to believe God’s promise. Don’t look within yourself. Introspection is a bottomless pit. Look instead to God’s promise. He guarantees eternal life to all who believe on Him for it. How simple!
Let’s review: Neither your good works, nor your circumstances, nor your feelings will give you assurance. Those things are all changeable and undependable. Only one thing will give you assurance: believing God’s testimony concerning His Son. God guarantees that all who believe on His Son for eternal life have it and will never perish. If you believe in Christ for eternal life, then you are sure that you’re saved. It’s that simple.