동서남북에 있는 문을 말하나, 천태종에서는 진성 (眞性)의 이 (理)에 증득 (證得)해 들어가는 문으로, 유･공 (有)･(空), 역유역공 (亦有亦空), 비유비공 (非有非空)의 사문( 四門)을 말함. 또 천태종에서는 사교 (四敎)에 각각 사문 (四門)이 있다하여 사교사문 (四敎四門), 즉 화의사문 (化儀四門)과 화법사문 (化法四門)을 이야기하기도 한다. 그런가 하면 또 밀교 (密敎)의 만다라 (曼茶羅)에서는, 사방 (四方0을 일컫는 말로, 동쪽의 발심문 (發心門), 남쪽의 수행문 (修行門), 서쪽의 보리문 (菩提門), 북쪽의 열반문 (涅槃門)을 뜻하기도 함

The four gates: It means the east, the west, the south, and the north, but they have many different meanings according to the Buddhist sects and teachings. The first theory of Tientai Sect: The gradual progress toward understanding of the true nature of things-- from the idea of existence to non-existence, from non-existence to affirmation of both existence and non-existence, and then from there to neither non-existence nor non-non-existence.
The second theory of the Tientai Sect: Four kinds of teaching according to the modes of teaching, four kinds of teaching according to the form of truth. Yet in the mandala of Esoteric Buddhism, four doors mean four directions, the east, the west, the south, and the north. The east signifies an initial aspiration for enlightenment, while the west signifies cultivation of the mind. The south signifies enlighten- ment, and lastly the north signifies Nirvana.