Four-Line Verse In Diamond Sutra

“Whatever has a form,
As a whole, is all illusory.
If you see all form as no-form,
Directly you see the Tathagata (Buddha-as-it-is).
That one raises a sincere faith on the Four-Line Verse in Diamond Sutra is not just a formal request for belief. If one could discern a core word out of this four-line verse, he would be the one who has really raised sincere faith.”
What is a core word of this Four-Line Verse?
What is the way to discern this one word?