Paul writes to the church in Galatia,
So Jesus revealed his gospel to Paul. When did Paul receive this revelation? During his Damascus experience? If so, why was that not recorded? Hence, we interpret that Paul is saying that he received this revelation later, in secret. For if it were in the open, then there would be no debate on Paul’s gospel - nor his apostleship.
Paul wrote to the Colossians,
Consider, if the mysteries of God were revealed through the single man Paul, as he claims, then on what grounds should we dismiss other people claiming the same thing? This sets up a dangerous precedent for us.
Surely then we can trust Ellen White of the Seventh Day Adventists, for she says she had visions from God. We can also trust Muhammad, who said he received visions and visits from angels. We can also trust Joseph Smith, who also claimed the same.
But in actuality, we cannot. Jesus said,
Since Paul did not receive his revelations in the open, then we must assume Jesus’s warning about those saying they found him in secret chambers is true in relation to Paul.
Value of this Evidence
This is decent evidence against Paul. The fact of the matter is that Jesus could have publicly called Paul to be an apostle like he did with the other apostles, but he did not. However, Jesus spoke against those who claim to find him in secret places, which applies to Paul.