These Believers differentiated themselves from polytheism in all its forms. The one belief that there is only one God was crucial. Thus Christians who believed in the Trinity would be excluded: “Those who say that God is the third of three, disbelieve; there is no god but the one God …” (Q 5:73). Hence, for example, Christians from communities who had originally fled persecution in Byzantium for refusing to believe in the Trinity were certainly welcome, and we know that Jews were, too. Christians who followed the Gospels, Jews who obeyed the laws of the Torah and converts from paganism who obeyed the injunctions of the Qur’an would all be included.
This ecumenical community was perhaps easier to achieve since the majority in the community would have been illiterate, and most likely only the most basic ideas were held between them. “It is fair to assume that most of the early Believers probably knew only the most basic and general religious ideas we today can find articulated in some detail in the Qur’an. That God was one, that the Last Day was a fearful reality to come (and perhaps to come soon), that one should live righteously and with much prayer, and that Muhammad was the man who, as God’s apostle or prophet, was guiding them in these beliefs.” (Muhammad and the Believers, Fred M. Donner).
Foremost the community strove to live a pious life. They saw this life as a preparation in a sense for the Last Day or Day of Judgment; it should be lived in obedience to God’s word as now laid out in the revelations of Mohammad. They believed that throughout man’s history God has from time to time revealed his intentions to a series of messengers or prophets of whom Mohammad was the last. Their steps towards inner purity included prayer, charity, fasting and pilgrimage. Distractions from the path of piety could include even family: “wealth and sons are the ornaments of the nearer life; but enduring works of righteousness are better before your Lord…” (Q 18:46), a passage that is somewhat reminiscent of a saying of Jesus from the Gospel of Thomas. In another passage the Qur’an appears to contradict it: “O you who Believe, do not forbid the good things that God has allowed you,” (Q 5:87) but the passage goes on to say: “nor go to extremes, for God does not love those who go to extremes.” Their piety was to be always with them as a source of balance and harmony, part of their everyday life. They were to be: “In the world, not of the world.”