Take a look at vv. 29-35.
29And the Spirit said to Philip, “Go over and join this chariot.” 30 So Philip ran to him and heard him reading Isaiah the prophet and asked, “Do you understand what you are reading?” 31 And he said, “How can I, unless someone guides me?” And he invited Philip to come up and sit with him.
32 Now the passage of the Scripture that he was reading was this:
“Like a sheep he was led to the slaughter and like a lamb before its shearer is silent, so he opens not his mouth. 33 In his humiliation justice was denied him. Who can describe his generation? For his life is taken away from the earth.”
34 And the eunuch said to Philip, “About whom, I ask you, does the prophet say this, about himself or about someone else?” 35 Then Philip opened his mouth, and beginning with this Scripture he told him the good news about Jesus.
Philip, upon arriving on the scene was prompted by the Spirit to run up to the chariot of the Eunuch. Running alongside it, he overheard the man reading from the Book of Isaiah chapter 53, which is “The Suffering Servant” prophecy. Upon hearing the reading of the Scriptures, Philip saw an inroad to this man to share with him the good news of Jesus Christ. Philip didn’t hesitate. He didn’t reflect, “Oh, this is an uncomfortable situation. He’s obviously an Ethiopian Eunuch. He’s a different race, a different social status, and he’s looked down upon by my people because he’s a eunuch.” No, Philip jumped right in and struck up a conversation with him about the text. In the course of that conversation, with Philip’s knowledge of Jesus Christ’s fulfillment of that prophecy, Philip was able to “tell him the good news about Jesus.”
So, what was the result of this divine appointment and the faithfulness of Philip? Look at vv. 36-38.
36 And as they were going along the road they came to some water, and the eunuch said, “See, here is water! What prevents me from being baptized?” 38 And he commanded the chariot to stop, and they both went down into the water, Philip and the eunuch, and he baptized him.
The Ethiopian believed the gospel! Still more, after trusting in Jesus Christ as his Lord and Savior, the Ethiopian eunuch asked Philip, “See, here is water! What prevents me from being baptized?” There was no reason. While the doors to the temple in Jerusalem were shut for him, the doors of the Kingdom of God were wide open.
The eunuch, in his faith in Christ, was now a full member of the one church of God (the body of Christ), baptized by the Holy Spirit, just like every other Christian. The prophesy in Isaiah had come to fulfillment. And, appropriately, Philip promptly baptized him with water.
On a side note – If you are a believer (a disciple of Jesus Christ) and have not been baptized, you should be. What are you waiting for? The Lord has commanded you be baptized. “What prevents you from being baptized?”
39 And when they came up out of the water, the Spirit of the Lord carried Philip away, and the eunuch saw him no more, and went on his way rejoicing.
I. Howard Marshall comments about this passage saying, “The way in which the story is told bears some structural resemblances to another story in which a Stranger joined two travelers and opened up the Scriptures to them, took part in a sacramental act, and then disappeared from view.” This stranger Marshall refers to was, of course, Jesus. Luke 24:27, the account of events on the road to Emmaus, tells us, “And beginning with Moses and all the Prophets, he interpreted to them in all the Scriptures the things concerning himself.”
The Gospel of Jesus Christ can be taught or preached from the starting point of any passage in the Old Testament (or the New, for that matter). Jesus demonstrated this to the two men on the Road to Emmaus, Philip did it from the passage in Isaiah to the Eunuch. And this is one of the reasons why I repeatedly ask, as we study the Old Testament together in the evening service, “Where is Jesus in this passage?”
The Eunuch would not have heard the message if not told it by another. Hence, the Lord called Philip and sent him to take care of it. Philip heard the call. He acted upon it. He was faithful in carrying out his calling. And the Lord blessed his obedience.