Modern physics successfully describes gravitational, inertial, and relativistic phenomena through highly predictive mathematical formalisms. However, the conceptual origins of gravity, inertia, mass, and the invariant speed of light remain largely unexplained, being treated as postulates or emergent coincidences. In this paper, we introduce the Fegrus framework, a structural interpretation in which gravity and inertia are not fundamental forces but manifestations of spatial coherence and phase alignment within a dynamically unfolding spatial structure. Within this framework, mass is reinterpreted as a measure of structural coupling between objects and space, while inertia and gravitation emerge as complementary responses to phase misalignment and spatial coherence pressure. Furthermore, the speed of light \( c \) is redefined not as a propagation velocity, but as a geometric boundary condition representing the maximal rate at which spatial structure can be coherently unfolded into three-dimensional observable reality. This reinterpretation provides a unified structural explanation for the invariance of \( c \), relativistic time dilation, length contraction, and the equivalence of inertial and gravitational mass. The Fegrus framework preserves the empirical success of classical mechanics, general relativity, and quantum mechanics, while offering a deeper conceptual foundation from which their mathematical structures naturally arise.