In the pre-Islamic period or Jahiliyyah الجَاهِلِيَّة, Arabs were not all monotheists. Like many other nations at the time, they had more than one faith دَيَانَة. Quraish قُرِيْش and neighboring tribes were principally paganist وَثَنِي. Judaism was the main religion in Yemen. Across different tribal regions, Individuals and small groups practiced Hanifiyyah الحَنِيْفِيَّة Abrahamic faith. In addition to being practiced by individuals in different tribes, Christianity was the majority religion in Najran and Northern Syria. Also, there were few magi in north east of Arabia.
For almost three hundred years before Islam, Khuza’ah tribe قَبِيْلَة خُزَاعَة were the guardians of the House of Worship بَيْتُ الله. It was their leader, Amro ben Luhi, who introduced paganism to Arabs. In a journey he made to Biladu sh-Sham بِلادُ الشَّام, modern-day Syria and Jordan, he came across people who were worshiping idols الأَصْنَام. He asked them for one so that he could take back with him and install it in the House of Worship. They gave him an idol called Hubal. Upon his return to Mecca, he set it up inside the Kaaba.
Due to Amro ben Luhi’s affluence and extraordinary generosity, he was highly honored among the Arabs such that whatever he said or did was willingly followed including idol worshiping. During pilgrimages, it was widely propagated that by worshiping Hubal and other idols, Arabs would be much closer to God. Idolatry was embraced by most tribes to the extent that every tribe started to have their own idol. These idols had different shapes. For example, the idol of Hamdan and Himyar was an eagle statue, the idol of Ghadafan was a female figure, the idol of Aws and Khazraj was a mere rock called manah. The practice of worshiping statues continued till the emergence of Islam.
As for Judaism, it is believed that it emerged in the Arabian Peninsula during the first century AD. Some of the Jews migrated from Palestine due to the oppression of the Romans. However, the majority of Arab Jews were converts. Small groups lived in Yathrib, present-day Madinah, but most of them lived in Yemen. The Himyarite people were predominantly Jews until the 525AD when the Romans sent a huge Christian army from Habesha, present-day Ethiopia, to occupy Yemen and eradicate Judaism. Though they succeeded in destroying the Himyarite kingdom, Yemenis continued to believe in Judaism until the emergence of Islam at the start of the 7th century AD.
According to the Quran, the Abrahamic faith was neither Jewish nor Christian. It was a true Arab monotheistic faith. In the Jahiliyyah, Arab followers of Abrahamic faith circumcised their babies, made pilgrimage to Mecca, avoided idols, maintain ritual purity, did not eat the meat of animal that were slaughtered as sacrifice to idols, and avoided alcohol. Although they were small groups and individuals scattered across the tribal regions, they shared these teachings. However, prior to the introduction of idolatry by Amro ben Luhi, it is said that all Arabs were followers the Abrahamic faith.
Arab Followers of Zoroastrianism were mainly concentrated in Hirah, located in the south-west of Iraq. Al-Hirah was ruled by Lakhm tribe. The Lakhmis were strong allies of the Sasanian empire, and it was through this alliance that some Arab Lakhmis became magi. Through trade, tribal relations, and alliances, other Arabs became acquainted with the religious practices of the magi. Some embraced this faith and believed in the unique influence that fire had in their lives. However, followers of this religion were restricted to Hirah and few groups scattered across Arabia. In other words, it was not as popular as other religions.
As for Christianity, it was embraced by individuals and small groups in different tribes across Arabia. Only the Najran, presently located in the south of Saudi Arabia, and northern Syria were predominantly Christian. Yemeni tribes in Najran were in constant conflict with other Yemeni tribes that were mostly Jewish. Therefore, Najranis sought help from Christians in Habesha. This resulted in mass conversion to Christianity. Arab Christians in northern Syria were from Quda’a and Azd tribes that migrated from Yemen in the 3rd century AD. Upon their settlement in the region, they converted to Christianity.
In summation, long before the emergence of Islam in Mecca and Madinah, Arabs were followers of the Abrahamic faith, i.e. Ahnaaf أحْنَاف. This is evident in their annual pilgrimage to Mecca from the time of Abraham till the early days of Islam. Their conversion to other religions and faiths was due to historical, tribal, and social events and conflicts.