Angels can fail because God allows them to make decisions and they are lesser beings than the perfect God. They can go astray, but the task is legitimate. God never tells they aren't allowed to instruct people - "just shut up and babysit them".
Michael S. HeiserWhat I mean by context is worldview - having the ancient Israelite or first-century Jew in your head as you read. How would an ancient Israelite or first-century Jew read the Bible - what would they be thinking in terms of its meaning? The truth is that if we put one of those people into a small group Bible study and asked them what they thought about a given passage meant, their answer would be quite a bit different in many cases than anything the average Christian would think. They belonged to the world that produced the Bible, which is the context the Bible needs to be understood by.
Michael S. HeiserRebellion against God results in being cast out of his service. God doesn't run the affairs of the spiritual world or our world with rebels on his payroll. They are cast to the Underworld (in the case of the Eden rebel), or a special place in the Underworld (e.g., the offenders of Genesis 6:1-4, who are, to quote Peter and Jude, "kept in chains of gloomy darkness" or "sent to Tartarus"). There are more divine rebels than that in the Bible, but hopefully that scratches the surface enough.
Michael S. HeiserWe think "reading the Bible in context" means thinking about the handful of verses before and after the verses we're looking at on the page. That isn't the case. While that's important, context is so much wider than a handful of verses.
Michael S. HeiserThe truth is that we don't know much about the spiritual world except for what Scripture tells us, so it's unwise to think we can speak with clarity about what a divine being can or cannot do. The tools of analyzing the natural world are of no use for analyzing the supernatural world. For the latter we need rules of logic, and the supernatural beliefs of the biblical writers are quite defensible in that arena.
Michael S. HeiserWe like to pretend the core ideas of the faith are more palatable or workable within our modern rationalistic approach to Scripture than the stuff we want to call "too weird" because of our own intellectual sensibilities. The truth is they are not. So we come up with interpretations to eliminate the weirdness of the biblical worldview that makes us uncomfortable. Problem solved!
Michael S. Heiser