Textual analysis: Lehi clearly states that he is citing information that he has read, and this information certainly comes from the brass plates. However, it is not clear from our Old Testament record what Lehi might have been reading. The specifics of a fallen angel do not appear in our texts until the New Testament. Our received Old Testament does indicate a Satan that exists before the Garden, because he is not mentioned as part of creation. Isaiah 14:3 hints at the events of the council in heaven, but are not sufficient to understand that council without modern revelation. This appears to be a point on which there were teachings in the brass plates that once again (like Zenos and Zenock) have not arrived to us in our texts.
Doctrinal analysis: Lehi's understanding of the role of Satan is quite clear and consonant with the understanding aided by modern scripture. Lehi's brief exposition provides the essential information about Lucifer's career: he was an angel, he fell from heaven, and tied up in his fall were circumstances which changed him from angel to devil.