仁王經疏 3.270

3.270

釋曰：第三、位分齊也。謂信忍住，通在三地，此當第二，故名中忍。謂此位中，無量為首，通修諸行。

Explanation: Third, the limits of the stage. The abide of faith-patience extends across the three bhūmis; this corresponds to the second, and is therefore called middle patience. In this stage, with the immeasurables foremost, one comprehensively cultivates all practices.