In Acts 1:8 Jesus says that the Gospel will first be preached in Judea and then spread to Samaria before eventually reaching the whole world. In chapter 8 we have some examples of the spreading of the gospel beyond the confines of Judea. To understand what’s going on it’s important to know that Samaritans are Jews of “mixed blood” because of intermarrying with other races, but trace their heritage to the same common ancestors; racially they’re part Jewish. Proselytes, as in the case of the Ethiopian, are Gentiles with no racial connection to Jews who have converted to Judaism and are considered members of Israel through religious conversion. So the gospel is going from the core of Israel to its very fringes without actually moving out to the Gentiles (no racial connection/non-converts) just yet.