Linked from
The 28 pages that link to Covariant derivative, each with the reason it gives.
Differential geometryRelated: It is the practical differentiation tool supplied by a connection.
Einstein field equationsRelated: It defines the conservation law compatible with curved spacetime.
Gauge symmetryRelated: It lets local symmetry coexist with derivatives in the equations of motion.
DivergenceRelated: Its trace defines divergence for vector fields on curved spaces.
Levi-Civita connectionRelated: The connection is the structure that defines this derivative.
Pauli equationRelated: It packages electromagnetic minimal coupling into a gauge-covariant operator.
Principle of covarianceRelated: It lets differential equations remain tensorial in curved spacetime.