妙法蓮華經玄義 1.30

1.30

宗者，要也。所謂佛自行因果，以為宗也。云何為要？無量眾善，言因則攝；無量證得，言果則攝。如提綱維，無目而不動；牽衣一角，無縷而不來。故言宗要。

"Purport" means the essential. It refers to the cause and fruit of the Buddha's self-practice serving as the central purport. Why is it essential? Immeasurable wholesome qualities are subsumed when cause is spoken of; immeasurable realizations are subsumed when fruit is spoken of. It is like hauling the main cord of a net, where no mesh fails to move; or pulling one corner of a garment, where no thread fails to follow. Therefore it is called the essential purport.