Original: Charlotte has the idea of writing words in her web extolling Wilbur's excellence ("some pig", "terrific", "radiant", and eventually "humble"), reasoning that if she can make Wilbur sufficiently famous, he will not be killed.
Simplified: Charlotte has the idea of writing words in her web showing Wilbur's excellence (like "some pig"), saying that if she can make Wilbur famous, he will not be killed.