They're the only characters, and these two are clearly meant to mirror and reflect each other at least somewhat. And towards the end, their connection is reasonably clear.
The banker is a man who is all about the material world and the comforts that money has to offer. The lawyer, on the other hand, wants nothing to do with anything physical and rejects pleasure, wealth, and every other earthly thing. The problem of course, is that they are both just the extremes of the spectrum, and the fact that they're opposites doesn't particularly help the reader or demonstrate a useful way to be. Where's the middleman?