Well I guess that those Ethiopians and others got it wrong when they tested their books against scripture and concluded they were scripture.
You sound like a useful person to have around and may be able to solve some old theological controversies. Can I ask is I Jn 5:7-8 Scripture?
— King James Version (1611)
Likewise the longer ending to Mark (Mk 16:9-20)
The issue is not whether Ethiopians, Syrians, Romans, Protestants, or anybody else looked at writings and reached a conclusion. Men can conclude many things. The question is whether God has spoken.
That is the line Scripture draws.
“For ever, O LORD, thy word is settled in heaven” ~Psalm 119:89. Not settled by a council. Not settled by a church body. Not settled by age, numbers, or religious tradition. Settled in heaven.
“Every word of God is pure: he is a shield unto them that put their trust in him” ~Proverbs 30:5. Then the very next verse gives the warning: “Add thou not unto his words, lest he reprove thee, and thou be found a liar” ~Proverbs 30:6.
That is the fear of God missing in a lot of these discussions. People handle the Word of God like it is a religious artifact to be managed by institutions, instead of the living truth before which every man must bow.
Jesus did not say the church cannot be broken. He said, “the scripture cannot be broken” ~John 10:35. Jesus did not say tradition sanctifies. He said, “Sanctify them through thy truth: thy word is truth” ~John 17:17.
So when someone says, “This group tested their books and concluded they were Scripture,” my answer is simple: that conclusion still has to bow to God’s Word. Man does not breathe out Scripture. God does. “All scripture is given by inspiration of God” ~2 Timothy 3:16. The word “inspiration” means God-breathed. Scripture comes from God, not from religious approval.
Now to 1 John 5:7-8 and Mark 16:9-20.
Scripture does not give us a verse saying, “This exact printed wording of 1 John 5:7-8 is original.” Scripture does not give us a verse saying, “Mark 16:9-20 is original.” So I will not pretend God has spoken where He has not spoken.
But hear this clearly: no doctrine of God hangs by a thread from a disputed wording.
If someone questions the wording in 1 John 5:7, the truth about the Father, the Son, and the Holy Ghost does not fall to the ground. Jesus commanded baptism “in the name of the Father, and of the Son, and of the Holy Ghost” ~Matthew 28:19. John said, “the Word was God” ~John 1:1. Thomas said to Jesus, “My Lord and my God” ~John 20:28. Peter said Ananias lied “to the Holy Ghost,” and then said, “thou hast not lied unto men, but unto God” ~Acts 5:3-4.
So do not act as though the truth of God needs one disputed phrase to survive. It does not.
The same with Mark 16:9-20. If someone raises a question about the longer ending, the resurrection of Jesus Christ is not hanging from that passage alone. The angel said, “He is not here: for he is risen, as he said” ~Matthew 28:6. Luke records, “The Lord is risen indeed” ~Luke 24:34. John records Thomas seeing the risen Christ and saying, “My Lord and my God” ~John 20:28. Paul says plainly, “Christ died for our sins according to the scriptures; And that he was buried, and that he rose again the third day according to the scriptures” ~1 Corinthians 15:3-4.
So again, no doctrine falls.
What does fall is the attempt to use textual questions as a smoke screen against the authority of Scripture.
The real issue is this: will we let God’s Word judge every human claim, or will we let human claims sit over God’s Word?
That is not a small issue. That is rebellion dressed in religious language.
Clear Scripture must govern the harder questions. Where Scripture speaks, we speak. Where Scripture is silent, we stop. And where men try to add weight to their claims by appealing to religious bodies, old traditions, or historical majorities, we answer with Scripture: “Let God be true, but every man a liar” ~Romans 3:4.
God’s Word judges man. Man does not judge God’s Word.
So if you are asking whether those passages should be used as the foundation for doctrine by themselves, no; doctrine must rest on clear Scripture confirmed by the whole counsel of God’s Word.