大方廣圓覺修多羅了義經略疏 1.346

1.346

若唯一度，未展虔誠；若過於三，禮煩則亂。故三周終始，顯示真心。佛雖已知，垂範應爾。

[Commentary:] If only done once, devout sincerity would not be expressed; if exceeding three times, cumbersome ritual becomes disorderly. Therefore, doing so through three cycles from end to beginning displays his sincere mind. Although the Buddha already knew, setting an exemplary model should be like this.