In verse 31

And he said, “Well, how could I [understand] unless someone guides me [correctly]?” And he invited Philip to come up and sit with him.

The Ethiopian eunuch all the while read the scriptures without understanding, but when Philip joined him by the leading of the Holy Ghost, he received speedy understanding.
This is why we have been given the Great Commission, to preach the gospel of Christ unto the ends of the earth.