 The proton is key to helping us understand the origin of mass. The only stable elementary particles in the proton with mass are the two up quarks and one down quark. Their tiny masses constitute only 1% of the mass of the proton. 99% comes from the energy of the fields and motion of the moving parts following the famous E equals MC squared formula. So it is quite accurate to say that confined energy is the origin of mass. We'll bring this point home when we get to the Higgs boson.