An odd thing happens in the gospels, Jesus forgives sins, and tells them to sin no more.
The implication is, I believe, sin is still possible even after accepting Jesus initially. But wait ! Jesus has the answer if in fact she does sin again, [confession].
**Maybe we should define our terms. Perhaps that will help this discussion and avoid confusion or misunderstanding.
When we say “salvation,” we (or at least I) mean deliverance or rescue from hell. I know that word encompasses a lot more, but for our present purposes, let’s say just that. When I say “being saved” or just “saved” I mean it to refer to a person who has received God’s free gift of salvation, which was received when the person repented and accepted Jesus as Savior and Lord. That is to say, he repented of sins and embraced the Person and Work of Christ at Calvary as payment for
his sins (not just the sins of the whole world, but of
his sins personally). That person, I believe, may be considered on the road to heaven. From a spiritual point (not physical), he is already there (Phil 3:20; Eph. 1:3).
When I say “assurance of salvation,” I mean having received the salvation God gives as a free gift and knowing that you have received it and presently possess it and are therefore on the road to heaven. I would also add, though you may not, that, knowing he is on that road, he will, by God’s grace and help and keeping power, remain on that road to the day of his death.
Now, the question you have raised is, what about the sins that occur
after receiving God’s free gift of salvation? Yes, Jesus told the woman, Go and sin no more. And that is what He tells us as well. He forgives us when we repent and accept Him. But He also wants us to “go and sin no more.”
1 John 1:7 to 2:1 deals with that. It is written to Christians and says:**
1:7. But if we walk in the light as He is in the light, we have fellowship with one another, and the blood of Jesus Christ His Son cleanses us from all sin.
8. If we say that we have no sin, we deceive ourselves, and the truth is not in us.
9. If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.
10. If we say that we have not sinned, we make Him a liar, and His word is not in us.
2:1. My little children, these things I write to you, that you may not sin. And if anyone sins, we have an Advocate with the Father, Jesus Christ the righteous.
** In the above passage, we see two things that deal with sins committed after conversion, after salvation. One
we do, and the other
Christ is doing. We do the one every time we sin, and He is doing the other, as we speak. We confess, and He is our Advocate or High Priest before the Father.
I think you are taking out of context the vine and branches passage of John 15. When we as believers sin, we do not get removed from the vine. That passage is talking about fruitfulness, not sin. There, bearing fruit is evidence of being a branch connected to the vine, the source of life. Without that connection (salvation), there is no life and therefore no fruit. On the other hand, committing sin is not evidence of
not being saved, for as 1 John 1:8 says of believers, “If we (believers) say we have no sin, we deceive ourselves and the truth is not in us.” It is a fact of life that we as believers sin, but that does not undo our salvation; it simply disrupts our fellowship with God, just as a small child may steal some cookies and then hide from his parents. He is still their child, but any closeness has been disrupted. Confession to the parent and resulting forgiveness restores that closeness and fellowship. Likewise with us, our confession to the Father restores our fellowship with Him. When we became believers we were given everlasting life as a free gift, which does not last only till we sin, or it could never be called “everlasting.” But sin must nevertheless be dealt with, just as a parent deals with their child, by spanking or otherwise. In the believer’s life, that is called chastening or chastisement (see Heb. 12:5-11), and will occur if we have unconfessed sin that
we have not dealt with (“if we would judge ourselves, we would not be judged” 1 Cor. 11:31).
So, the bottom line is, we can know we are saved and on the road to heaven. John said,** ** “These things I have written 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 continue to believe in the name of the Son of God.”(1 John 5:13)**