How could Paul say he was more than the other ministers of Christ?
Paul could speak as he did because he received further revelations from the risen, ascended Christ, not merely the pre-crucified Christ. Those later revelations gave his apostleship priority, much like a later will supersedes an earlier one. That is why he could say he was more, while still insisting he was nothing in himself.
Les explains that Paul's humility shows through, since he continually says he is nothing. Yet Paul asks, "Are they ministers of Christ? I speak as a fool, but I am more." Les says the reason he could say that is the revelations he received—not from the pre-crucified Christ, but from the Christ after the death, burial, resurrection, and ascension. That makes all the difference. Les illustrates it with wills: if a 1980 will is later replaced by a 1990 will, the courts look at the last one. So it is with Paul's apostleship: he had not walked with Christ as the others did, but he had further revelations, and at a later time he over and over becomes the primary apostle. Les also notes that cults misuse this idea, saying their leader came long after Christ and therefore has more authority, though he says it is valid only up to a point.