King Saul's early success lay in the fact that he looked like a king. As it turned out, looks were deceiving. Jesus saw in James, Judas, Simon, and Matthew the potential that others could not see. Not only are there surprising names on the list. Jesus surprisingly changed three of their names, giving them nicknames.
Nicknames are interesting.
Sometimes they are given because they do not fit. Most often, they are given because they do fit. He did not seem much like a rock. He was changeable and undependable. But Jesus knew what he was going to become.