When someone decides to walk away and/or gets into sin and sin deceives them and they are turned over to a reprobate mind as spoken of in the first part of Romans where God said they refused to retain the knowledge of God.
1 John 3:8-9
He who sins is of the devil, for the devil has sinned from the beginning. For this purpose the Son of God was manifested, that He might destroy the works of the devil. 9 Whoever has been born of God does not sin, for His seed remains in him; and he cannot sin, because he has been born of God.
So, to your point: someone who decides to get into sin: of the devil.
My point: born of God: verse 9: DOES NOT sin; CANNOT sin.
The guarantee is from God's side, and He keeps the door open to repentance so He does His part... unfortunately, He cannot force someone to continue walking with Him should they decide to backslide since He is the One who gave people the right and ability to make their own choices.
You are right about one thing: the guarantee is from God.
It isn't that your flesh daily walks in sin. It is that Jesus' blood washes you clean and God sees your through that blood: in His reckoning you CANNOT sin.
If this were not true, satan wouldn't be trying to choke the Word out of our lives like Jesus said he is in Mark 4:14-20
Satan most certainly is trying. Let's look closely:
Mark 4:14-15
The sower sows the word. 15 And these are the ones by the wayside where the word is sown. When they hear, Satan comes immediately and takes away the word that was sown in their hearts.
The sower sows the Word. This is the preaching Christian.
The ones by the wayside. Hmm. The unsaved. Satan is trying to keep them away from becoming saved.
Let's look at another:
mark 4:18-19
Now these are the ones sown among thorns; they are the ones who hear the word, 19 and the cares of this world, the deceitfulness of riches, and the desires for other things entering in choke the word, and it becomes unfruitful.
Thorns. Pricking us, hurting us. This is the Christian who keeps one foot in the world. The Word is choked. And he becomes unfruitful. Unfruitful is not lost; it is unfruitful. Without fruit. Lacking a good witness. Kinda like the Prodigal Son. He's out having fun in the world but he's still a son. He'll be welcomed with a big hug when he comes to his senses.
People do it all the time. So, if a Christian backslides and lives after the flesh rejecting God going forward, you think they still go to Heaven?
When a true Christian is saved, he is changed. His desires are changed. Sure they may wander away from under God's wing and get pricked by the thorns but Jesus ALREADY washed their sin. When I do what I know not to do, according to Paul in Romans 7, it is not me but rather it is sin within me.
My new man is clean and righteous. This is the real me. My old man has a desire for things in the flesh. Sanctification is helping me to overcome this side. Doesn't mean I won't stumble. But in God's eyes, I'm washed in the blood and I CANNOT sin (1 John 3:9).
If so, then you must all believe that as long as someone says with their mouth they believe in Jesus... they can live like the devil the rest of their life and still go to Heaven even though they rejected a relationship with God.
A regenerated man will have no such desire. A man who intellectually chooses God but does not make a heart commitment certainly can (and will) embrace the sin of this world.
You make a straw man here, Ted. A saved man is changed and has no desire to "live like the devil.". He who sins is of the devil. He who is born of God CANNOT sin. I have yet to find a believer in "lost salvation" who can rectify these verses into their theology. These verses are speaking about salvific actions: if you are born of God then you CANNOT sin.
In Galatians 6:7,8 God specifically said WHATSOEVER a man sows, that shal he also reap. Reckon God lied or somehow doesn't know what He's talking about? Maybe God failed to control what went in to His book?
In 1 John 3:9 God specifically said: if you are born of God you will not sin, you CANNOT sin. Reckon God lied or somehow doesn't know what He's talking about.
Galatians says that we reap what we sow. If as a Christian we step off God's path for us and embrace things of this world, we will become unfruitful. We sill suffer lack. We may become sick. There is nothing there about going to hell. You lose the protection and benefit; you don't lose the relationship. In fact, nowhere in Galatians 6 does it speak of being lost. To the point that at the end of the chapter Paul tells us that in Grace Jesus is with your spirit. He keeps you. His Holy Spirit guides you.
God is not looking to cut you loose when you stumble. He simply is not that petty.