Linked from
The 19 pages that link to Stress–energy tensor, each with the reason it gives.
GravitationRelated: It represents the energy and momentum that source spacetime curvature.
Vacuum energyRelated: Its vacuum expectation value determines how vacuum energy gravitates.
Curved spacetimeRelated: It supplies the matter-and-energy content that sources curvature.
Positive energy theoremRelated: Energy conditions are stated as restrictions on this tensor.
Ricci calculusRelated: Its components form the matter side of Einstein's tensor equations.