大乘百法明門論開宗義決 1.103

1.103

若變心等便無用等者。等即等取諸心所法。何故變心無實用耶。故下二句釋此義云。相分心等不能緣故。若變心等即是相分。既相分心無能緣用。故賴耶識不變心等。

Regarding "if it transformed into mind, etc., it would lack utility, etc.": "Etc." includes by extension all caitta dharmas. Why would transforming into mind lack real utility? The following two clauses explain this meaning, saying: "because mind, etc. as nimitta-bhāga cannot take objects." If it transformed into mind, etc., they would be nimitta-bhāga. Since a mind that is nimitta-bhāga lacks the function of taking objects, the ālayavijñāna does not transform into mind, etc.