This is the understanding of thus topic so far, will be subject to change when I have more understanding.
This is another degree of freedom or dimension in particle. The proton and neutron mass are very similar. And beside of the mass, and electric charge, proton and neutron are the same in everyway. Thus, it was portuslated that they are same particle and the different of mass is due to the electronmagnetic field. Which is like the Zeeman splitting of energy level on spin.
And also, the proton-neutron interaction is same as neutron neutron interaction in most cases. Thus it strongly suggest proton and neutron are same particle under strong interaction.
Without an magnetic field. Energy level of different spin are degenerated. And same thing happen on isospin : when there is no charge, no electric field, the energy level of isospin will be the same. So, proton and neutron will be the same particle when there is no field. And the strong force does not charge sensitive, thus, under the strong force, proton and neutron are the same.
spin and isospin share same mathematic description.
a magnetic moment, it can be come from spin angular momentum or orbital angular momentum, whic is current distribution.
The electric moment can be generated by isospin and electric charge distribution.