According to this thesis, Shaka preached Kegon-kyo Sutra (Avatamska Sutra) first but as it was too difficult for people to understand, he preached Agon-kyo Sutra (Agama Sutra) next which was easier.
最初に華厳経を説き、その教えが難しいため人々が理解できなかったとして、次に平易な阿含経を説いたとする。