This paper presents a novel, comprehensive theoretical framework, rigorously rooted in the Foundational Substrate Theory (FST), aimed at fundamentally explaining the nature of the gravitational force and its potential unification with other fundamental interactions. This framework definitively diverges from General Relativity's geometric interpretation , proposing instead that gravity emerges from the dynamic, attractive interaction between Standard Matter particles (M) and their hypothesized inherent counterparts, Complementary Matter particles (CM). These entities operate within a dynamic Foundational Substrate (FS), whose intrinsic properties, governed by the comprehensive FS field, dictate all interactions. We axiomatically postulate that CM possesses properties precisely opposite to M (e.g., negative mass, mCM=-mM\( \), as dictated by the "Law of Zero") and that their kinematics are universally linked by the fundamental axiom \( V_c⋅V_p=c^2 \). This axiom rigorously dictates that CM particles associated with slow-moving M particles possess extremely high, effectively superluminal velocities (VC), leading to a vast effective "Radius of Motion" (Rm) or influence range.This characteristic, quantified by the Motion Environment Ratio \( (R_m∝c^2/(V_P^2 )) \)\( \), is proposed as the direct explanation for the long-range nature and profound relative weakness of gravity compared to other fundamental forces (electromagnetic, strong, weak), which primarily arise from direct M-M interactions. The inherent M-CM symmetry and the postulated attractive nature of the interaction between positive and negative mass/energy entities within this framework, dictated by the Law of Zero and mediated by the FS field, ensure the universal attraction of gravity. FST further offers a unified perspective on the origin of dark matter (as tightly coupled \( M+CM \)) and dark energy (as \( E+CE \)), and provides a robust resolution to gravitational singularities. This model offers new, quantifiable perspectives on force unification, entropy, and the transition between particle existence and the substrate state at the critical speed c. While requiring further rigorous mathematical development to derive the exact value of the gravitational constant G from FS principles, the theory presents a compelling pathway towards a fundamental, quantum description of gravity originating from precise particle interactions within a dynamic Foundational Substrate.