Paul must stress that the gospel he proclaimed came "straight from the horse’s mouth" (no blasphemy intended). He is an ambassador of Christ who has been directly and personally commissioned.
And this is the bottom line, isn't it? Are we dealing here with one human tradition alongside many or is the gospel proclaimed by the apostles truly a matter of divine revelation? If it is the latter, the authentic Christian faith is in a different ball game from competing religious traditions.
Do we have something special? Maybe we try to avoid this claim for fear that others might think we consider ourselves superior. Indeed, the apostle Paul is sometimes accused of being arrogant. But he includes himself in the anathema: cursed is everyone who falsifies the truth – myself included, if I come to you with a “gospel” different from what I brought to you at first and which you received at first.
It would be arrogant to think that we know the truth perfectly and exhaustively or that others have no idea about anything. But knowing the truth is not arrogant, even if it is truth about something really quite important. Wanting to share the truth is generosity not superiority.
If we are confident that Christ is “the way, the truth and the life”, we want to say so. If we are not, we do well to go back to basics. What is our good news?