俱舍論頌疏論本 3.2

3.2

分別根品者，勝用增上故名為根。此品廣明，故名分別。所以界品後次明根品者，界品明諸法體，根品明諸法用，依體起用，故次明根。

Regarding the 'Chapter on Discrimination of the Indriyas': because their superior function is predominant, they are called 'indriyas'. This chapter explains them extensively, hence it is called 'discrimination'. Why the Indriya Chapter is explained directly after the Dhātu Chapter: the Dhātu Chapter explains the substance of phenomena, while the Indriya Chapter explains the functions of phenomena; because functions arise based on substances, the indriyas are explained next.