Deference between Listener.ora, tnsnames.ora and sqlnet.ora in Oracle

Listener.ora: >  When an instance starts, a listener process establishes a communication pathway to the Oracle

database. The listener is then able to accept database connection requests.

Tnsnames.ora: > This is a configuration file that contains net service names mapped to listener protocol addresses, or net service names mapped to connect descriptors for the local naming method.

Sqlnet.ora: > This file is the profile configuration file. It resides on the client machines and the database server. Profiles are stored and implemented using this file. The database server can be configured with access control parameters in the sqlnet.ora file. These parameters specify whether clients are allowed or denied access based on the protocol.