首楞嚴義疏注經 5.155

5.155

初作不淨想，後入骨鎖觀，皆為治貪。復因骨鎖，入析色明空。復因此空，見色實相，悟中道理。色之與空唯一實性，故云空色二無。

First he made the visualization of impurity, and afterwards entered the contemplation of the skeleton; both were to remedy greed. Further, through the skeleton, he entered the analysis of form to clarify emptiness. Further, through this emptiness, he saw the real mark of form and awakened to the principle of the middle way. Form and emptiness are only one real nature; hence he says, 'both space and form became nonexistent.'