While I believe the Bible teaches conditional eternal security, we can, and should have absolute assurance of our salvation:
12 He that has the Son has life; he that does not have the Son of God does not have life.
13 These things I write 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 believe in the name of the Son of God. EMTV (1 Jn 5:11-13)
Whenever I share the gospel with someone, I normally share these verses. The Bible is clear, that if we have the Son of God as our Savior, then we know that we have eternal life. John wanted his readers to know that the reason why he wrote this book, was to provide them with a basis for having assurance of their salvation.
Throughout the book of 1 John, the apostle states many things that provide a means for determining whether a person is truly saved or not. 1 John is like a test for determining true salvation, and this is needed because many have a mistaken idea of what faith is.
The Apostle John defines faith for us in many ways, coming at it from different directions. But generally speaking, John defines faith as obedience. The outworking of faith is a sincere commitment to Christ and His will. It’s what I teach on this website. Read the book of 1 John, and you will see that this is the overall teaching of the book.
We can determine whether we have true biblical faith by examining what we regard to be faith in light of what 1 John teaches. If we can honestly say that our faith and lives reflect what John teaches there, then we can have total assurance of our salvation. If Christ is the center of our lives because of faith in Him, and our lives are clearly moving in a Christ-ward direction, then we can be assured that the faith we have is a biblical faith.
However, if while reading 1 John, we see that our lives don’t line up with what we say we believe, then quite likely, there’s an absence of salvation. It’s a false faith, a faith that does not save.
Spiritual inventory should be taken often to make sure our faith is where it should be. 1 John is a great place to start.