"Indeed, those who have believed and those who were Jews and the Sabi'un (Sabians) and the Christians - those who believed in Allah and the Last Day" - meaning: those of them who believed in Muhammad and entered into his religion and his law.
Muhammad said: There is a difference of opinion regarding the nominative case (raf') of the word "al-Sabi'un". The best view is that it is understood as being postponed and is in the nominative case by virtue of being an initial subject (ibtida'). The meaning is: "Indeed, those who have believed and those who were Jews - whoever believed in Allah and the Last Day and did righteousness - then no fear will be upon them (fol. 86), and [likewise] the Sabi'un and the Christians."