How was it preached and what factors contributed to its spread ? To answer these questions, one sociologist goes so far as to say that since Islam preaches human equality, which is different from the caste system that had been introduced with Hinduism, it could easily penetrate into Indonesian life in a silent manner, teaching that all people are equal on account of their having been created by the same Almighty God (Wertheim 1950). Another factor that may have promoted the spread of Islam is that the Indonesian mind can easily adopt Islam and feel at home in it. Islam offered the ordinary Indonesian a way of thought that had its attractive aspects, without forcing the mind to do what it is unable to do (Van Nieuwenhuijze 1958:73). Similarly, the ability of the early preachers of Islam to win converts was enhanced by the use of techniques which rendered their message more familiar to their audience; the use of wayang, a sort of shadow play helped communicate their teachings (Djajadiningrat 1958:378). Nurman Said (2010:15) who cited S.Q.Fatimi (1963: 78) wrote that, in attempting to make the people of Java interested in Islam, the Wali Songo (the nine walis) tried to combine persuasive methods of preaching with the arts of diplomacy and healing. The Walis are often associated with Sufi saints who were able to perform miracles, thereby impressing their audiences and convincing them of the superiority of Islam over their own religion. Some of the Wali Songo earned their livelihood through trade.