This is a simile, but its meaning is unclear. These words could refer to 1) a baby that is born unexpectedly early, in which case Paul means that he was unexpectedly called to be an apostle, or 2) a baby who is born early and is very small, in which case Paul means that he had not learned from Christ and grown spiritually as the other apostles had, or 3) a baby who is born dead, in which case Paul means that Christ appeared to him when he was spiritually dead. (See: [[rc://en/ta/man/jit/figs-simile]])