It is your human understanding and opinion that man, once saved can become not saved by not believing.
that is not God's take on it.
Do you realize how condescending this sounds? How do you know it is not your "human understanding" that causes you to believe in OSAS? I would be happy to believe in OSAS if I could find it in Scripture. Honestly, I would prefer for it to be true (just as I would prefer universalism to be true), but I reject it because the Scriptures seem to plainly teach that true believes can (and do) fall away and abandon the faith.
In John 14:4 what it talks about is bearing fruit for the Lord. That is not a loss of salvation.
I assume you meant to cite John 15:4-6. Yes, it does have to do with bearing fruit, but it is also saying more than that. Jesus is speaking of those who are in union with Him being cut off. Believers bear fruit because the life of Christ flows into them just as the life of a vine flows into the branches. Jesus says that branches that are cut off "wither" and are then burned. If a branch "withers" that means it previously had life in it, but no longer. And Jesus doesn't say "fruit" withers and is burned (destroyed), but "branches"
which were believers "in Him" [the Vine].
So the language simply will not fit with your interpretation (human understanding?)
Romans 11:23 those branches do not believe in Christ. Those are the people who believe in Judaism and still await their Messiah.
Look at the passage again. Paul is speaking of the ancient olive tree which represents God's covenant people. Those who are broken off form the olive tree are broken off from God's people. Only God's people are saved. Unbelieving Jews are broken off because of unbelief. Because they reject Christ, they are cut off from God's people. They no longer belong to God. After explaining this, Paul says to the Gentiles "but you stand by faith." But then he immediately warns them that they can be broken off just like the unbelieving Jews if they do not continue in the faith. There is no way around the language. They stand by faith, but can be broken off through unbelief just as the unbelieving Jews were broken off.
Glatians 5:4 are not seeking Jesus Christ and His grace for salvation, but are seeking the Old Covenant law to be good enough. When one seeks to be made righteous through the law, that person turns their back on grace.
But it says more than that. It says they are severed (cut off) from Christ. There is no life outside of union with Christ. There is no salvation outside of His grace.
We cannot be cut off from God once we are saved.
God's gifts are irrevocable.
I need to get going, so I will just quote sometime I wrote on this passage a while back in a post at my site:
Romans 6:23; 11:29
For the wages of sin is death but the free gift of God is eternal life in Christ Jesus our Lord….For the gifts and the calling of God are irrevocable.
Many see here a strong assertion of unconditional eternal security based on the fact that “the gifts and calling of God are irrevocable” (NAS), and that eternal life is a gift (Rom. 6:23; Eph. 2:8, 9), therefore, they reason, eternal life must be irrevocable. God is always faithful to his promises (both pleasant and terrible, e.g. Joshua 23:15, 16), but his promises are not without conditions. God’s gift of salvation is irrevocable
so long as the condition is met. Paul was speaking of Israel’s final restoration in Rom.11:29, but he was giving no assurance to those branches that had been broken off in unbelief (verse 20), and sternly warned that those who
were now standing by faith, could yet be broken off through unbelief (verses 20, and 21). God’s divine gift (of life) is
always and only for believers! God does not revoke his gift, for it cannot exist outside of Christ. Only believers are “in Christ Jesus our Lord” (Rom. 6:23). If we fail to meet the condition for union with Christ, we can have no claim on the gift (see Jn. 3:16 and 10:27-29 discussed above).