大乘起信論義記 2.80

2.80

言以離念境界等者，釋無相所以也。若妄念所緣，是則有相；既唯真智之境，明知無妄執之相也。釋真如門竟。

The words 'because it is a realm free from conceptual thought' and so forth explain the reason why it is without marks. If it were the cognitive object of delusional thoughts, then it would possess marks; since it is solely the realm of true wisdom, one clearly knows that it is devoid of marks of delusional attachment. The explanation of the gate of tathatā is completed.