You may not agree with what I'm going to say. It requires a lot of Bible study.
There's this matter called predestination that comes around with a lot of speculation at times. In Ephesians and Romans, Apostle Paul says those called was from the foundation of the world, and are elect. But in Matthew 24:24 Jesus specifies a deeper elect group He calls the "very elect". And Jesus shows those "very elect" cannot be deceived.
In Matthew 22:14 Lord Jesus makes a distinction among believers, saying many are 'called', but few are 'chosen'. In John 17, Lord Jesus reveals that His 'chosen' sent ones, His Apostles, were owned by The Father originally, and The Father gave them to Jesus, and He sent them into the world, which is the meaning of the word for apostle, to be sent. This makes a distinction between those 'called' only, compared with those who are 'chosen'. Per Acts 9, Jesus said that Saul (became Paul) was His "chosen vessel", making Paul His Apostle.
When Jesus first met His Apostles and commanded them to follow Him, they left off what they were doing and immediately followed Jesus. That shows ownership. Because Paul was actually hunting down Christians on the road to Damascus when Jesus struck Paul blind and spoke to him, that means Jesus directly intervened with Paul, removing his doubt about Him and Christians. That does not happen for every believer. It mostly happens only with those who are 'chosen'.
Yet in Apostle Paul's Epistles, he is constantly reminding those in the Church to remain focused on Christ, and don't become apostates by falling away. Paul would not preach that falling away warning if those could not fall away. So if those believers can still fall away from Jesus, then it means those are not... 'chosen', but 'called' only. One who is called only can... still fall away from Christ, is what that means. It strongly suggests that Christ's "very elect" represent His chosen ones that cannot fall away.
In Revelation 13:4-8, we are shown the "dragon" (devil) will have power over all nations and peoples at the end of this world for 42 months, and the whole... world will worship him, EXCEPT those who names were written in the book of life from the foundation of the world. Which believers would that be, the called and the chosen, or just the chosen of His "very elect" that can never fall away? It is the latter, Christ's "very elect" that cannot fall away. They are chosen, He already owns them, which is why He can directly intervene in their lives.
This is why there is confusion in The New Testament about the predestined elect and the called elect. It's a matter of one is innocent until proven guilty; those called only are deemed elect until or if they fall away. And per Paul in 2 Thess.2, there will be many believers that will fall away once the coming "man of sin" shows up in Jerusalem exalting himself as God in the Jew's new 3rd temple.
This is why it will only be the "very elect" that will reject the coming false-Messiah who will play Jesus at the end. They already know who that coming "man of sin" will be (he ain't here yet today either).