When I say INFJ, I'm currently just talking about the test, not the functions stuff (which I view as a separate theory).
INFs in general are prime candidates for psychology, because e.g. IN is most correlated with introspection, and F adds to it (people who pay attention to their feelings tend to on average be more in touch with their inner psychologies too).
Basically F also induces a level of people-orientation.
Js somewhat exceed Ps in terms of being a bit more willing to be normative and/or prescriptive, i.e. "this is how things ought to go" which can attract them to counseling people, but at the same time, Myers suggests that a lot of people want to be listened to with a more P attitude, i.e. an attitude that just listens to what's there, rather than prescribing.