大乘起信論義記 1.114

1.114

如是此論文句雖少，普攝一切大乘經論旨，故云總攝如來廣大等如理智境，故云深也；如量智境，故云廣也；深廣無際，故云無邊也。

Thus, although the sentences and phrases of this śāstra are few, they universally subsume the purports of all Mahāyāna sūtras and treatises; hence it says "summarily subsume the vast, profound... of the Tathāgata." Being the realm of cognition of things as they are, it is called "profound"; being the realm of cognition of the extent of things, it is called "vast"; being boundless in depth and vastness, it is called "boundless."