A "chicken or the egg" question

Which comes first, faith or understanding?

In Romans 10:14-15 Paul creates a logical chain of thoughts:

14 How then will they call on him in whom they have not believed? And how are they to believe in him of whom they have never heard? And how are they to hear without someone preaching? 15 And how are they to preach unless they are sent? As it is written, “How beautiful are the feet of those who preach the good news!”

Then in verse 17 he says, "So faith comes from hearing, and hearing through the word of Christ."  So belief comes after understanding and understanding only comes after gaining knowledge.  Yet while you cannot believe without knowledge, knowledge alone will not lead to belief.  Knowledge will lead to understanding and understanding to faith only after God does a work of regeneration on our heart.

Someone might say, "I don't have to understand the Trinity to believe in it," or on a less spiritual note, "I don't have to understand how my car works in order for me to drive to work."  I'd reply, you don't have to understand every detail about how your car works--pistons, carburetor and all--but you do have to have some amount of understanding that your car was designed to transport you from A to B before you can have faith your car will take you someplace.

Consider this story from Acts 8 about Philip and the Ethiopian eunuch:

26 Now an angel of the Lord said to Philip, “Rise and go toward the south to the road that goes down from Jerusalem to Gaza.” This is a desert place. 27 And he rose and went. And there was an Ethiopian, a eunuch, a court official of Candace, queen of the Ethiopians, who was in charge of all her treasure. He had come to Jerusalem to worship 28 and was returning, seated in his chariot, and he was reading the prophet Isaiah. 29 And 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. 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. 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.

You see the eunuch did not receive faith until after he began to understand Isaiah.  This is why it is so important to develop your understanding of Christianity through things like reading the Bible and listening to sound teaching that explains the Scriptures.  It is like putting a plant in an environment where it can flourish, watering it often, and giving it lots of sunlight.

It seems so formulaic but it's important to recognize God's sovereign election and activity in this story because without it the Ethiopian eunuch would not have come to faith--even with Philip's explanation.  God's hand is evident in that a) Philip's presence on that specific road was the result of obeying the instruction given to him by an angel of the Lord, and b) God had no purpose for Philip on that road other than to meet the eunuch.  We know this because after his meeting with the eunuch Philip was immediately taken away by the Spirit of the Lord to another place.