The extended and precise investigation of the nucleon (spin) structure is a cornerstone of the EIC initiative; the availability of deuteron and $^3$He polarized beams will offer unprecedented opportunities to obtain information on the neutron spin structure comparable to those of the proton; the combination of these data will allow to deepen knowledge and understanding of many aspects of the nucleon spin physics: from a more precise test of the Bjorken sum rule to a more detailed picture of the flavor structure of the nucleon sea, as well as a precise determination of different spin and transverse momentum dependent functions, at leading and higher twists. Moreover, almost close kinematics and large acceptance detectors typical of a collider, will potentially offer new measurement perspectives beyond the asymmetries.