金光明經文句記 6.49

6.49

二、約坐夏答。既開後安居免於坐秋，則前安居人得立迦提月。廢秋之意，為此二緣。

Second, answering in terms of sitting the summer retreat. Since the later retreat is inaugurated, freeing them from sitting in autumn, practitioners of the earlier retreat can establish the kāthina month. The intention behind eliminating autumn is due to these two conditions.