The first council also defined the set of rules (Vinaya) that governed the life of monks and nuns within the monastic community.
[2] The late Professor Hirakawa Akira says that the First Council collected only short prose passages or verses expressing important doctrines, and that these were expanded into full length suttas over the next century.
[3] There are five nikayas (collections) of suttas: This includes The Greater Discourse on the Foundations of Mindfulness, The Fruits of the Contemplative Life, and The Buddha's Last Days.
According to Keown, "there is considerable disparity between the Pāli and the Sarvāstivādin versions, with more than two-thirds of the sūtras found in one but not the other compilation, which suggests that much of this portion of the Sūtra Piṭaka was not formed until a fairly late date.
"[4] This is a heterogeneous mix of sermons, doctrines, and poetry attributed to the Buddha and his disciples.