Come and hear, all who fear God;
I will tell what he did for my soul:
to him I cried aloud,
with high praise ready on my tongue.
Psalm 65 
'It is written in the prophets:
They shall all be taught by God,
and to hear the teaching of the Father
and to learn from it,
is to come to me.'
. . .
"How can I...unless I have someone to guide me?" Indeed. I am conscious, as I reflect on the words of Scripture, of my own training. Not my professional training, but my formation as a Christian. What I have learned from the theologians I have read and studied does influence my reading of the Bible, but that reading is shaped much more profoundly by my upbringing in Christ, from the influence of my mother to the conversations around the table as I studied the Gospel according to Mark in college. I continue to be guided by the picture of Jesus that has been imprinted in my mind and embellished and corrected through the years. No matter whether I am alone or in company when I am actually reading the Bible, I am always surrounded and guided by the many witnesses to Jesus who have led me on the way.
And the witnesses have all, in some way, done for me what Philip and the psalmist have done: to tell the Good News of what God has done. The words Jesus speaks in John's Gospel seem even more enigmatic in this context: how is it that we can be 'taught by God,' except through the words of God's witnesses? One could certainly make the argument that the eunuch in Acts 8 is taught by God, who uses Philip for the purpose. Philip is instructed by the Holy Spirit to approach the chariot, and then is spirited away after baptizing the eunuch. What, exactly, Philip says, we don't know. (Ok, so I don't know. Maybe there are commentators who are fairly certain. But that's not really my point here.) Presumably, Philip connects the passage in Isaiah 53 to Jesus, and explains Jesus further with some reference to what has been going on in Jerusalem recently. Maybe he gives his own testimony as a part of that.
The real mark of the eunuch's having been 'taught by God', though, is in the response. He comes to Jesus by his baptism. This seems to me to be the heart of Christian formation, of all the guidance that we ought to give and receive on the journey of faith: to be led to Jesus, again and again. However far we stray, however short we fall of our intention to follow him, we can be restored by Jesus.
So it is right that the psalmist calls out in his need, making supplication to God, and at the same moment is ready to praise him: he 'cried aloud' in hope that God would save him, and so afterward proclaims what God did for his soul. I pray that hope will live in me, as it has been formed by the witness of so many like him. For those who have taught me by word and deed, I will always be thankful.