The HL7v2.x Message Profile Repository is the part of the HL7v2.x external validation service which contains all the message profiles and tables needed to validate messages.
Actually, when you use the External Validation Service (EVS Client) to validate your message, you are asked to provide the context in which this message is sent, it means domain, actor, transaction, and message type. This context enables the validator to retrieve the profile your message must be validated against.
Profiles and resources (data tables containing the codes for Sex, Religion and so on) are XML files referenced by an OID.
The HL7v2.x Message Profile Repository provides a Web Service interface to retrieve and submit message profiles and resources.