What is the main security service a cryptographic hash provide?

'Ease of computation' is a performance characteristic of hash functions, not a security service; it does not describe a security guarantee provided to users of the hash.

Message authentication is provided by an HMAC (keyed-hash message authentication code), which combines a hash with a secret key - a plain cryptographic hash alone provides no authentication because it has no secret component.

Collision resistance is an important property but it is a technical construction requirement (hard to find two inputs with the same hash), whereas computational infeasibility (pre-image resistance) is the direct security service that protects confidentiality of the input and supports integrity.

Integrity is the core security service - a hash allows any party to verify that data has not been modified by recomputing and comparing the digest. Computational infeasibility refers to pre-image resistance, meaning it is practically impossible to derive the original input from the hash output alone. These two properties together define the fundamental security guarantees of a cryptographic hash function as described in NIST FIPS 180.