Linked from
The 23 pages that link to Lambda calculus, each with the reason it gives.
FunctionRelated: It gives functions a precise role in the foundations of computation.
Type theoryRelated: Lambda calculus supplies a core language for many type theories.
Bound variableRelated: Lambda abstraction uses the same scope-based notion of variable binding.
Church–Rosser theoremNarrower topic: The theorem is a central property of its untyped version.