That verse from acts is probably not a good one to justify the view that you need SOMEONE to teach what the bible says:
Philip and the Ethiopian
26 Now an angel of the Lord said to Philip, “Go south to the road—the desert road—that goes down from Jerusalem to Gaza.” 27 So he started out, and on his way he met an Ethiopian a eunuch, an important official in charge of all the treasury of Candace, queen of the Ethiopians. This man had gone to Jerusalem to worship, 28 and on his way home was sitting in his chariot reading the book of Isaiah the prophet. 29 The Spirit told Philip, “Go to that chariot and stay near it.”
30 Then Philip ran up to the chariot and heard the man reading Isaiah the prophet. “Do you understand what you are reading?” Philip asked.
31 “How can I,” he said, “unless someone explains it to me?” So he invited Philip to come up and sit with him.
32 The eunuch was reading this passage of Scripture:
“He was led like a sheep to the slaughter,
and as a lamb before the shearer is silent,
so he did not open his mouth.
33 In his humiliation he was deprived of justice.
Who can speak of his descendants?
For his life was taken from the earth.” b
34 The eunuch asked Philip, “Tell me, please, who is the prophet talking about, himself or someone else?” 35 Then Philip began with that very passage of Scripture and told him the good news about Jesus.
36 As they traveled along the road, they came to some water and the eunuch said, “Look, here is water. Why shouldn’t I be baptized?” c 38 And he gave orders to stop the chariot. Then both Philip and the eunuch went down into the water and Philip baptized him. 39 When they came up out of the water, the Spirit of the Lord suddenly took Philip away, and the eunuch did not see him again, but went on his way rejoicing. 40 Philip, however, appeared at Azotus and traveled about, preaching the gospel in all the towns until he reached Caesarea.
What we see is thatan angel told Philip go go to this road, the SPIRIT then told Philip to walk alon side the Eunach and when Philip noticed him reading Isiah, Philip asked if he understood ( the prophecy) and the Eunach said he didn't because he had no one to teach him ( about the prophecy) and WHO it applied to ( Isiah or someone else), Philip then explains that it is about Jesus and speaks to the Eunach about Jesus, the Eunach then, obviouslytouched by the HS, accpetes Jesus and at the moment, is Baptized. Right after that Philip is "wisked" away to Azotous and the Eunuch went on his way rejoicing.
The lesson is NOY that SCRIPTURE needs to be taught or needs someone else to interpret, but that prophecy needed, in this case, to be understood and Philip HELPED with that and the Eunuch believed because of Philp AND the HS.