華嚴一乘教義分齊章 1.26

1.26

二、約攝方便。謂彼三乘等法總為一乘方便，故皆名一乘。所以經云「諸有所作，皆為一大事故」等也。

Second, by reference to gathering up expedients (upāya). That is to say, the teachings of the Three Vehicles and so on altogether constitute upāya for the One Vehicle, and therefore are all named the One Vehicle. Hence the sūtra says: "Whatever is done is all for the sake of the one great matter," and so forth.