Some proponents of the King James Version-only position (often called "KJV-onlyism") like FEBC may believe that Christians who use modern Bible translations have compromised their faith.
There are several issues to separate:
1. Does using another Bible version mean someone has "lost their faith"?
From a mainstream Christian perspective, no. Most Christian traditions—including many evangelical, Reformed, Baptist, Anglican, Lutheran, Methodist, and Catholic churches—accept multiple faithful translations of the Bible. They argue that:
The original Hebrew, Aramaic, and Greek manuscripts are inspired by God.
Translations vary in wording because languages differ, not necessarily because translators reject God's Word.
A Christian's faith is demonstrated by trusting Christ and following Him, not by exclusively using one English translation.
Someone may prefer the KJV for its literary beauty or translation philosophy without believing other translations are illegitimate.
2. How does perseverance fit into this?
If a KJV-only advocate says, "People who leave the KJV have lost their faith and therefore were never truly saved," they are usually reasoning from a doctrine like the perseverance of the saints.
In that framework:
True believers persevere in the truth until the end.
If someone permanently abandons what they consider essential truth, they conclude that person was never genuinely converted.
However, this creates another question:
Is exclusive use of the KJV an essential doctrine of Christianity?
Most Christians would answer no. They would distinguish between:
Essential doctrines: the Trinity, the deity of Christ, His death and resurrection, salvation by grace through faith.
Secondary doctrines: Bible translation preference, church governance, worship style, and similar issues.
If KJV exclusivity is not an essential doctrine, then changing from the KJV to another faithful translation would not be evidence that someone has failed to persevere in saving faith.
3. How would a KJV-only proponent respond?
A strong KJV-only advocate might argue:
God has perfectly preserved His Word in the KJV.
Modern translations corrupt key doctrines.
Therefore, abandoning the KJV is abandoning God's preserved Word.
Someone who does so may show spiritual decline or even reveal they were never truly converted.
Not all KJV advocates go this far. Many simply prefer the KJV and do not question the salvation of Christians who read other translations.
4. How would others respond?
Christians who reject KJV-onlyism would typically say:
Perseverance concerns remaining faithful to Christ, not remaining loyal to one English translation.
A believer can faithfully read translations such as the New King James Version, English Standard Version, New American Standard Bible, or New International Version while fully affirming biblical authority.
The doctrine of perseverance cannot be used to prove that every disagreement over Bible translation indicates apostasy.
Conclusion
The claim that "those who use other Bible versions have lost their faith and are not persevering to the end" is a theological assertion held by some KJV-only proponents, not a conclusion that follows directly from Scripture or one accepted across Christianity. Whether someone is persevering in the faith is generally understood to be about continuing to trust and follow Jesus Christ, rather than about exclusive allegiance to a particular English Bible translation.