The community was larger and more developed, in contrast to its minority position in Mecca.
Due to the new circumstances of the early Muslim community in Medina, these surahs more often deal with details of moral principles, legislation, warfare (as in Surah 2, al-Baqara), and principles for constituting the community.
and at times directly address Muhammad or speak of him as "an agent acting in combination with the divine persona: 'God and his messenger' (Q 33:22)".
Classification of the surahs into these periods is based upon factors such as the length of the verse and the presence or absence of certain key concepts or word (e.g. al-Rahman as name of God).
While the themes of the Meccan surahs remain, the Muslims growing into more of a community and the formation of Ummah, now is clear.