One problem is believers who think other believers cannot come to faith and then go back to the world.
1 Cor 6:9-10
Do you not know that the wicked will not inherit the kingdom of God? Do not be deceived: Neither the sexually immoral nor idolaters nor adulterers nor male prostitutes nor homosexual offenders nor thieves nor the greedy nor drunkards nor slanderers nor swindlers will inherit the kingdom of God.
1 Cor 5:11
But now I am writing you that you must not associate with anyone who calls himself a brother but is sexually immoral or greedy, an idolater or a slanderer, a drunkard or a swindler. With such a man do not even eat.
The gospel is about God telling us He is willing to deal with us as friends, as people blessed by Him.
John 15:14-15
You are my friends if you do what I command.
I no longer call you servants, because a servant does not know his master's business. Instead, I have called you friends, for everything that I learned from my Father I have made known to you.
Now to be given this great privilege, the highest and greatest gift in all creation and to reject it outright, would be ignored by God is absurd. The root problem is unbelief in knowing the power of the gift, the depth of the love involved, and the freedom to overcome sin we now have.
There is a simple explanation for people who walk away from God. They were never saved in the first place. God doesn't lose those he has called, ever! These people were never called, so therefore they were not saved. You have just quoted John, Jesus' talking to the disciples. But John also wrote the following words.
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They went out from us, but they did not really belong to us. For if they had belonged to us, they would have remained with us; but their going showed that none of them belonged to us." 1 John 2:19
I cannot judge whether someone is saved. They may seem to be on fire for God, even reading their Bibles and then just walking away. But God knows their hearts. If they do sin willfully, and know it is wrong, how are they following Christ? A relationship with God is based on him calling us, then justifying us. And we do have to obey him. Repentance is what God gives us to do. But, God is the one who calls us. We do not have the ability to call ourselves because we are dead in our sin.
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because those whom he foreknew he also predestined to be conformed to the image of his Son, that his Son would be the firstborn among many brothers and sisters. 30 And those he predestined, he also called; and those he called, he also justified; and those he justified, he also glorified." Romans 8;29-30
This is called the "Golden Chain of Salvation." There is no hint of losing your salvation, because you sinned or walked away. A believer can't be lost, or that makes their actions more important than our Heavenly Father. God saves us, we do not save ourselves. I never knew this truth for 25 years, because I had attended Arminian Churches. It didn't reflect my salvation experience or anything I had read in the Bible.
Then came terrible Rheumatoid Arthritis, which was painful and deforming, and I was not diagnosed properly or treated properly. I was also condemned and judged by Word Faith people because I didn't have enough "faith" to be healed. I was broken, and turned away from God. I don't mean I started sinning wantonly, I stopped my daily Bible readings, prayer, and attending church. Basically, I turned away from my wonderful relationship with God. I was hurt and angry. But somehow, I knew God was standing behind me. He wasn't going to allow me to sulk forever. After 2 years, I heard the voice of God telling me to read 5 Psalms a day. At first, I was disobedient. I didn't read the Psalms, or anything else. But God kept telling me to read 5 Psalms a day. I finally started reading 5 Psalms a day. I found real people! Hurting, rejoicing, sinning and being restored, can you say David? I read 5 Psalms a day for 2 years. That is all of the Psalms every month x 24. It was restorative to my faith. By then I was back walking with God, doing my devotions and learning more about God then I ever did in my healthy days.
In fact God called me to seminary, to get an MDiv, and then a PhD program to help people who are suffering, which is all of us, in one way or another. So, did I lose my salvation or not? I did not! God is above time, and he had plans for my life, which I followed. In fact, the rest of Romans 8, shows us that we can NOT lose our salvation, not because of what we do, but because of God's love for his people.
"31 What then shall we say about these things? If God is for us, who can be against us? 32 Indeed, he who did not spare his own Son, but gave him up for us all—how will he not also, along with him, freely give us all things? 33 Who will bring any charge against God’s elect? It is God who justifies. 34 Who is the one who will condemn? Christ is the one who died (and more than that, he was raised), who is at the right hand of God, and who also is interceding for us. 35 Who will separate us from the love of Christ? Will trouble, or distress, or persecution, or famine, or nakedness, or danger, or sword? 36 As it is written, “For your sake we encounter death all day long; we were considered as sheep to be slaughtered.” 37 No, in all these things we have complete victory through him who loved us! 38 For I am convinced that neither death, nor life, nor angels, nor heavenly rulers, nor things that are present, nor things to come, nor powers, 39 nor height, nor depth, nor anything else in creation will be able to separate us from the love of God in Christ Jesus our Lord." Romans 8:31-39
This is the gospel, expanded. Paul speaks about this many times. It clearly says "Nothing will be able to separate us from the love of God in Christ Jesus our Lord." NOTHING! Think on that for a while. Instead of calling saved people to repent because they have "lost" their salvation, go preach to the masses who do not have that relationship with Christ. Stop judging and condemning Christians, and instead encourage them, by posting Scriptures that show how God will never leave or forsake us. In fact, the book of Hebrews which you keep twisting says that, quoting Deut. 8:6,8:
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Your conduct must be free from the love of money and you must be content with what you have, for he has said, “I will never leave you and I will never abandon you.” Hebrews 13:5
Or Ephesians:
"But God, being rich in mercy, because of his great love with which he loved us, 5 even though we were dead in offenses, made us alive together with Christ—by grace you are saved!— 6 and he raised us up together with him and seated us together with him in the heavenly realms in Christ Jesus, 7 to demonstrate in the coming ages the surpassing wealth of his grace in kindness toward us in Christ Jesus. 8 For by grace you are saved through faith, and this is not from yourselves, it is the gift of God; 9 it is not from works, so that no one can boast. 10 For we are his creative work, having been created in Christ Jesus for good works that God prepared beforehand so we can do them." Eph. 2:4-10
Read the whole chapter, as the first part is about how God saves our sin dead souls. There are many more verses in the Bible. You have a God who is weak, and cannot even keep his own people? You believe free will, including the will to sin and walk away, is more important than the sovereignty of God? I feel sorry you are so trapped in a wrong interpretation of this. I might try and comment later on your Hebrews passage, but this is too long already.
