2: The argument from the Apostles’ weakness.
If the apostles were making up a religion, they didn’t do it the way most founders of new religions have. They didn’t make themselves look great and worthy of respect. They made themselves look like a train-wreck.
“Far from showing us a community seized by a mystical exaltation, the Gospels present us with disciples demoralized (‘looking sad’) and frightened,” says the Catechism. “For they had not believed the holy women returning from the tomb and had regarded their words as an ‘idle tale.’ When Jesus reveals himself to the Eleven on Easter evening, he upbraided them for their unbelief and hardness of heart, because they had not believed those who saw him after he had risen.”
If they were making up a religion, they were doing it wrong, giving people reasons not to put faith in them.