Persecution against the church at Jerusalem pushed the disciples out of the city and into fulfilling the Great Commission (cf Mark 16:15; Acts 1:8). There are two specific references to the preaching that was done in the dispersion of Acts 8:4.
The first begins with a very simple statement, “Then Philip went down to the city of Samaria and preached Christ to them” (v 5). Later in verse 12 we read the following, “But when they believed Philip as he preached the things concerning the kingdom of God and the name of Jesus Christ, both men and women were baptized.”
This is a very simple sequence: Philip preached Jesus; the Samaritans believed what Philip preached; those who believed were baptized.
The second account also involves the preaching done by Philip. Called away from the great response in Samaria, Philip is commanded to go to the desert where he is presented with the opportunity to preach to one Ethiopian man, a Jewish proselyte, who was reading from the prophet Isaiah, specifically what we know as Isaiah 53.
Inquiring as to the subject of the text, the Ethiopian asks, ‘Is the prophet speaking of himself or of some other man?’ The text records that “Philip opened his mouth, and beginning at this Scripture, preached Jesus to him.”
In the very next verse, the Ethiopian, seeing a body of water, asks Philip, “See, here is water, what hinders me from being baptized?” Following his confession of Jesus as the Son of God, both he and Philip went down into the water where he was immersed.
Again, we see the same sequence: Philip preached Jesus; the Ethiopian believed what Philip preached; the Ethiopian was baptized.
This is exactly the pattern that Jesus set forth in the Great Commission: “Go into all the world and preach the gospel to every creature. He who believes and is baptized shall be saved; he who does not believe shall be condemned” (Mark 16:15-16).
One cannot preach the gospel or preach Jesus without preaching the necessity of baptism to be saved. This is why the gospel is God’s power to save (Romans 1:16).