A painter, and a terrible one at that, might seem to be the worst person to seek legal advice from, but in the world of The Trial, the best sources of insight are often the most unlikely ones. On the recommendation of a client, K. seeks out the counsel of Titorelli, a painter of mediocre landscapes and, more importantly, portraits of judges. It isn't so much Titorelli's personality that matters here as much as what he tells K. about the court system.
So why should the novel choose a painter as the voice of insight? Yes, it is outlandish for a painter to give legal advice, but the novel uses this artist figure as the voice of its own aspirations as a work of literature. Just like Titorelli's paintings, the novel is a work of art that reveals the truth about the way the world works. But Titorelli is a really bad painter. Couldn't the novel picked a better artist as a representative of its own aspirations?
The novel's ironic choice of artist figure could be due to its reluctance to set up anybody as a hero. Perhaps it is more important to look at how Titorelli is a bad painter. We learn that Titorelli isn't original: he paints according to conventions and rules handed down for generations, and he paints not out of a feeling of a special vocation, but because he inherited the post from his father. Titorelli's lack of originality is the voice of the novel's own concern that one of the consequences of the modern age is that all we can do is copy the people who came before us. Just as K. seeks an acquittal, something new and unprecedented that is only rumored to have happened in the past, true artists seek to create something different and new. If Titorelli is the face of modern art, then he's a terrible spectacle indeed, because to write – or paint – without the possibility of producing something new and original is certainly cause for despair.