Christianity.

Muhammed's contemporaries lived amid religious indifference. The
majority of the Arabs were heathen and their religious aspirations
were satisfied by local cults of the Old Semitic character. They may
have preserved the religious institutions of the great South Arabian
civilisation, which was then in a state of decadence; the beginnings
of Islam may also have been influenced by the ideas of this
civilisation, which research is only now revealing to us: but these
points must remain undecided for the time being. South Arabian
civilisation was certainly not confined to the South, nor could an
organised township such as Mecca remain outside its sphere of
influence: but the scanty information which has reached us concerning
the religious life of the Arabs anterior to Islam might also be
explained by supposing them to have followed a similar course of
development. In any case, it is advisable to reserve judgment until
documentary proof can replace ingenious conjecture. The difficulty of
the problem is increased by the fact that Jewish and especially
Christian ideas penetrated from the South and that their influence
cannot be estimated. The important point for us to consider is the
existence of Christianity in Southern Arabia before the Muhammedan
period. Nor was the South its only starting-point: Christian doctrine
came to Arabia from the North, from Syria and Babylonia, and numerous
conversions, for the most part of whole tribes, were made. On the
frontiers also Arabian merchants came into continual contact with
Christianity and foreign merchants of the Christian faith could be
found throughout Arabia. But for the Arabian migration and the
simultaneous foundation of a new Arabian religion, there is no doubt
that the whole peninsula would have been speedily converted to
Christianity.