You wrote the second part as if you were very sure about many things.
For if you really are not sure if there is a real difference between “internal” and “external”, how can you be so sure that oxytocin is “internal” and command of Jesus is “external”?
Now, of course, all that is easy for Thomists: we believe that soul maintains unity of the human body, in which oxytocin exists virtually, thus it is a part of human body - thus it is “internal”; we believe that Jesus is separate from us and thus “external”.
But do you believe in souls? Do you believe that the commands in question are given by real Jesus who is definitely separate from us?
A common atheist metaphysics will claim that we are not as real as the fundamental particles of which we consist. That we are mostly arbitrary collections of fundamental particles that interact in a complex way.
But in that case, why is one collection of fundamental particles (oxytocin) supposed to be “internal”, and a different collection (Church) - “external”? Not to mention that someone who obeys such commands is likely to be the member of the Church, and thus fundamental particles will be “shared”.
That’s what I’m pointing out when I ask if your metaphysics can handle this.
If that was the reason, you would be checking if believers or nonbelievers perform good works in a superior way according to some criteria.
That is much easier than the tortuous method you chose, and directly checks something you claim to be relevant.
Though, of course, the tortuous way has its advantages in the case when you fear what you will find in straightforward way…