I learnt that many things remained to be studied further, and I heard that many things still remain to be listened to' (included in "Shorai Mokuroku"): What Kukai brought back was the latest cultural system including Esoteric Buddhism.
「未だ学ばざるを学び、～聞かざるを聞く」（『請来目録』）、空海が請来したのは密教を含めた最新の文化体系であった。