妙法蓮華經玄義 2.78

2.78

三法妙者，謂總三法，縱三法、橫三法、不縱不橫三法、類通三法，皆祕密藏，故稱為妙。

The subtlety of the three dharmas: this refers to the comprehensive three dharmas, vertical three dharmas, horizontal three dharmas, neither vertical nor horizontal three dharmas, and categorially shared three dharmas. All are the secret storehouse, and therefore called subtle.