True Christians Cannot Lose Their Salvation

For example, The idea of the Book of Life is a figurative expression taken from the custom of registering citizens in a society or maintaining genealogical records." The genealogical sections of the Bible (such as 1 Chronicles chapters 1-9 represent the Book of Life for the nation of Israel. A family lineage is vitally important in OT culture, especially for the purpose of maintaining ownership of the family land. Thus, to be "blotted" out of the Book of Life meant the person's lineage would be forever removed from the genealogical record. We see examples of this with Korah's rebellion (Numbers 16), Achan's sin (Joshua 7), and the kingdom of Saul (1 Samuel 15).

Coming to the New Testament, the use of the phrase Book of Life takes on the meaning of a register that records all of those individuals who are "God's elect," who are to inherit eternal life. See for example Philippians 4:3, Revelation 3:5, 13:8, 17:8, 21:27. In Revelation 13:8 and 17:8, one factor that distinguishes between those written in the Book of Life and those who are not, is that those not written in the Book of Life are easily led astray by the Anti-Christ. Those who are written in the Book of Life will not follow the Anti-Christ.

What exactly does John mean in Revelation 3:5? John's words are describing an act of spiritual obedience. In other words, overcoming is a discipline believers perform in the course of normal sanctification. A continuing act of personal holiness out of love for God not to try to get saved but as evidence that true Christians are already saved & their manner of life verifies it.