Even if God is speaking metaphorically or in parables?
What about where we know there are errors, if taken literally, like the four corners of the earth?
A metaphor or a parable can and should have a literal interpretation applied to it. This is to say that the metaphor or the parable serves the main point of the passage, in some way, and the literal application of the metaphor or parable must serve the main point of the passage.
For instance...the parable of the Prodigal Son has one main point--it is to accuse and convict the Pharisees. There are several sub-points that can, and should, be brought out in preaching or teaching this parable, such as the son feeding pigs or the father running. These things, feeding pigs or the father running, would have shocked the audience and they show how low the son had fallen and how much the father loved his son. But, neither of these things "actually" happened, per se. Yet they serve the main point--to accuse and convict the Pharisees--and they serve to show God's love for his children.
Next, "Four corners of the earth" is not meant by the author to be scientific statement. Rather it is an idiom. In fact, it is an idiom we still use today to indicate "the whole earth."
How about when Paul says that he is speaking his own opinion and not it is not God speaking?
Are these ideas as literally true as when he speaks what God told him to say?
Again, we have to deal with the main point. Usually, when Paul speaks his opinion, his opinion serves the greater main point. We also have to remember that Paul, being an Apostle, giving his opinion carries much more weight than say Fred the Plumber giving his opinion.
Furthermore, we don't (or shouldn't) believe in direct inspiration of scripture. Rather, the more proper mode is "Verbal-Plenary Inspiration." This is why all of Paul's writings are similar in style, even if they vary stylistically.
How about the reversal of creation in Gen. 2 from Gen. 1?
This is not a reversal. The retelling of creation in Genesis 2 is a typical Hebrew discourse in which the reader/listener is re-focused on one aspect of the creation account. Obviously, in this particular discourse, it is the creation of Man.
A FURTHER COMMENT:
All interpreters of scripture have but one goal: To rightly divide the word of truth. In doing so, the interpreter must find the main point of any given passage and make that main point the main point of his preaching or teaching. Only then can the expositor rightly say "Thus says the Lord."
If we don't find the main point or if we don't acknowledge the main point even while preaching a sub-point of the text, we are doing violence to the text of scripture itself and we are putting our opinions out there as God's word--a very dangerous scenario.
The Archangel