Eison regarded a revival of the precepts and the study of Shingon Esoteric Buddhism as equally important, so he reprimanded his disciple Ninsho for being negligent of the study by being too enthusiastic about social activities and propagation in eastern Japan, and at the time of Mongol invasion attempts against Japan, he offered a prayer and ritual of Esoteric Buddhism at Saidai-ji and Shitenno-ji Temples to repel the Mongol Empirical army.
また、戒律復興と並行して真言密教の研究を重視しており、弟子の忍性が東国において社会活動や布教に熱を入れすぎて教学が疎かになっているのを窘めたり、元寇の際には西大寺や四天王寺などでモンゴル帝国軍撃退の祈祷や密教儀式を行っている。