This is a simple one to answer, and you should have several good examples of why this is important to an organization. Before we go into the purpose and goal of an IT Security organization, let's examine what you might encounter in a typical IT environment, and why a hiring manager is asking this question.

Depending on the size of the IT organization, the hierarchy might look something like this: CIO/CTO, VP(s), Director(s), Manager(s), Analysts, Developers, Testers, Project Managers, Architects, etc. Keep in mind that there will likely be non-technical team members in the IT department whose roles are to be a conduit or liaison between the business and the technology/security departments. You might be in a panel interview with three or more people from the company you are interviewing at, and one or two of those people might be a Business Analyst or Project Manager who may or may not have a technical background. The reason for this is to get a mix of technology/security and business personnel to participate and ask questions that might be relevant to their role. At the core of your response, your answer should be something like; helping the organization succeed, prosper or grow, and that security is needed to ensure the company runs smoothly and efficiently.