It's a done deal! Our old man is crucified with Christ!
Romans 6:6 Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin.
All who have trusted the Lord after hearing and believing the word of truth, the gospel of our salvation are saved and sealed!
1 Corinthians 15:1 Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand;
1 Corinthians 15:2 By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain.
1 Corinthians 15:3 For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures;
1 Corinthians 15:4 And that he was buried, and that he rose again the third day according to the scriptures:
...
Ephesians 1:13 In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise,
Ephesians 1:14 Which is the earnest of our inheritance until the redemption of the purchased possession, unto the praise of his glory.
That's eternal security if I ever heard it! And so is this:
Romans 8:29 For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren.
Romans 8:30 Moreover whom he did predestinate, them he also called: and whom he called, them he also justified: and whom he justified, them he also glorified. ( see also Eph 1:4 KJV)
Romans 8:31 What shall we then say to these things? If God be for us, who can be against us?
Romans 8:32 He that spared not his own Son, but delivered him up for us all, how shall he not with him also freely give us all things?
Romans 8:33 Who shall lay any thing to the charge of God's elect? It is God that justifieth.
Romans 8:34 Who is he that condemneth? It is Christ that died, yea rather, that is risen again, who is even at the right hand of God, who also maketh intercession for us.
Romans 8:35 Who shall separate us from the love of Christ? shall tribulation, or distress, or persecution, or famine, or nakedness, or peril, or sword?
Romans 8:36 As it is written, For thy sake we are killed all the day long; we are accounted as sheep for the slaughter.
Romans 8:37 Nay, in all these things we are more than conquerors through him that loved us.
Romans 8:38 For I am persuaded, that neither death, nor life, nor angels, nor principalities, nor powers, nor things present, nor things to come,
Romans 8:39 Nor height, nor depth, nor any other creature, shall be able to separate us from the love of God, which is in Christ Jesus our Lord.
Not believing in eternal security of the believer today is to wrongly divide the word of truth (2 Timothy 2:15 KJV) and/or listening to the religious, denominational deceitful worker (2 Corinthians 11:13-15 KJV).