法華玄義釋籤 2.54

2.54

餘趣會實諸經或有，二乘全無，故合菩薩對於二乘，從難而說，釋據盡理故須論九，斷此等疑，生一乘信。

The convergence of the other destinies into the real is sometimes present in various sūtras, but for the two vehicles it is completely absent. Therefore, combining bodhisattvas to contrast with the two vehicles is spoken from the perspective of what is difficult. The explanation, based on exhausting the principle, must discuss nine, so as to cut off these doubts and give rise to faith in the one vehicle.