首楞嚴義疏注經 1.340

1.340

既言因法有心，應知心本無體；無體言合，理必不然。一法云何合？斯之謂矣。

Since you say there is a mind dependent on phenomena, you should know that the mind originally has no substance. To speak of uniting when there is no substance is logically impossible. How could a single phenomenon unite? This is what it means.