Some Characteristics of the Early Buddhist Suttras:
1. Both the Nikayas and the Agamas come from original Buddhist texts, but they have been disseminated in two geographically different regions. They contain simple but very rich authentic Buddhist teachings.
2. Both were circulated orally for 400 years after the Buddha's demise.
3. There are a lot of narrations and repetitions in these texts. They reflect many customs, social and religious issues, life and thoughts at the Buddha's time.
4. They contain what the Buddha taught to the four groups of His Sangha (monks, nuns, Buddhist followers) about how to develop spiritually and how to live, behave and treat one another. All these teachings are simple and easy to remember.
5. They contain the fundamentals in Buddhism, the core from which all other Buddhist sects developed: the Four Noble Truths, the Dependent Origination, the Eightfold Path, Impermanence, Suffering, and No Self, and the spiritual development path of Disciplines, Meditation, and Wisdom. 6. For the first 400 years after the Buddha's demise there was no mention of Mahayana nor Theravada/Hinayana.
Sources:
http://www.daophatngaynay.com/vn/kinh-dien/pali/12329-Khai-quat-lich-su-truyen-ba-kinh-dien-va-nhung-dac-diem-cua-kinh-tang-Nikaya.html
http://en.wikipedia.org/wiki/Hinayana
http://en.wikipedia.org/wiki/Nikaya
