(James 3:6) And the tongue is a fire, a world of iniquity: so is the tongue among our members, that it defileth the whole body, and setteth on fire the course of nature; and it is set on fire of [by] hell.
Various translations translate this verse differently, but the general gist is as follows:
1. The tongue is a fire
In translating this literally we must consider how a part of the body can literally be a fire. Since this image is usually considered as a metaphor, this suggests that the tongue and the fire referred to are in the spiritual realm, since that realm contains symbols.
In phrase #5 below, we see that the tongue speaking wickedness is on fire; that is to say, it is a fire. If a piece of wood is on fire it is proper to say that it is a fire. After all, what is a fire if not something that is burning?
2. The tongue is a world of iniquity [among the parts of the body]
Since speech is the way we communicate our innermost thoughts of the heart, and since the tongue is one of the key organs of speech (vocal chords, mouth, and lips are others), it is proper to say that the tongue is the iniquity in our hearts that we express through our speech. This symbol of the tongue being iniquity is real in the spiritual realm since symbols have real substance in the spiritual realm. That is why Catholic devotions such as the Sacred Heart of Jesus are so awesome — the physical parts of the body are tangible symbols.
3. The tongue defiles the whole body [the whole person]
If one part of our body is defiled, so is all the rest. We can't pretend to be pure of heart if our tongue is on fire (because of our wicked words).
4. The tongue sets the course [cycle] of nature [of the person's life] on fire.
The tongue is a fire because it is on fire. When it comes in contact with all the other aspects of our life, it sets them on fire as well. As the wicked words leave the mouth and wreak havoc on others, the fire spreads to everything it touches, especially to our own bodies.
5. The tongue is set on fire by hell.
There are many passages in the Bible connecting hell and fire. Just as a person in hell will be literally burning, so also while alive on this earth, the spiritual body can burn. In this case, the literal spiritual fire of hell ignites the literal tongue of a person's spiritual body when they speak wickedly. This starts the chain of events of the other images.
In conclusion, there is no reason to resort to figures of speech or symbolic language to interpret this verse. All the images are easy to explain literally using my system of Philosophy and Creative Frame view of the universe. The following features: