Jesus tells us point blank whose words we are to believe. In His prayer to the Father, He prays for His Discipled Apostles, which were given to Him by the Father. And Jesus says that He prays for those who will believe THEIR WORD.
John 17:20
"Neither pray I for these alone, but for them also which shall believe on Me through their word"
What word is that, you ask?
Matthew 28:19
"teach all nations ... to observe all things whatsoever I have commanded you"
Anyone who is teaching contrary to what Jesus taught His 12, is not a disciple of Jesus. And the only records we have, given to us from people who walked with Jesus the whole time of His earthly ministry, are the books of Matthew and John.
Luke wasn't there, and tells you he pretty much acted like a journalist, picking and chosing who to talk with, and what to believe from their accounts... at best. For all we know, Luke talked with people who had an axe to grind.
Hearsay isn't even good enough in a court of law... hopefully, still. The same thing can be said about Mark... Mark wasn't a Discipled Apostle, either.
And if you think Jesus was correct in saying that by the witness of two or more people is anything established... Paul's entire account falls to the ground. In fact, much of what Paul said is either commentary ripped out of context, or plainly restated from the Prophets themselves. What does Paul say that the OT hasn't already said, or that Jesus hasn't confirmed from the OT?
By Paul's own account, he fits the description of the woe'd Pharisees who would persecute from place to place, scourge to make them blaspheme, and murder outright... having fit the Prophecy of Matthew 23, Paul stood condemned.
People want to think that no matter what they do, they can be forgiven by God, and that's why they believe Saul of Cilicia's completely unverified claim.
God doesn't break His own rules. Saul had no witnesses to bring. And it's ludicrous to believe his circular argument, that his story of witnesses validates the story itself. If God had wanted Saul as a witness of 'undeserved grace', He wouldn't have always said repent THEN believe.
Saul was still cursing the Son of God, when he was supposedly saved by grace alone through faith alone... Nonsense! faith in Jesus is required FIRST. That never happened to Saul.
And the people who think that Jesus left things undone and unsaid... or that everything changed when Jesus was murdered for His inheritance by the Pharisees... well, THESE are the ones who take the Pharisees word over that of Jesus Himself. They don't see at all what differences exist between the Gospel of the Kingdom and that blasphemous gospel of 'grace unearned', because the blind led the blind.
Grace unearned is anomia=without law, iniquity... "all things are lawful" to Saul.
Jesus says He will give to us according to our works, in Revelation... in Matthew, He says to observe whatsoever He taught and commanded us... these are our works.
And the Holy Spirit's job, according to Jesus, is to remind us of WHAT JESUS SAID, and to teach us what Jesus meant... What place has Saulianity's 'gifts'? NONE AT ALL.
Jesus says to go unto all the Nations and teach them... What job does that leave the self-annointed 'apostle to the gentiles'? ZERO.
Jesus says He is the good shepherd... What does that make Saul? A HIRELING... at best.