However in 813, when Saicho asked Kukai to lend "Rishushakkyo" (the interpretation book of "Rishu-kyo" (Principle of Wisdom Sutra)), Kukai refused to lend it saying that the essence of Mikkyo lay not in ascetic training of sentences but in practices, which led to worsen the relations between both of them.
しかし、弘仁4年（813年）最澄が『理趣釈経』（『理趣経』の解釈書）の借用を空海に申し出たところ、空海が密教の真髄は文章修行ではなく実践によってのみ得られるとして拒絶したため、両者の仲は悪化する。