ISO 27000 relates to Information Security Management System (ISMS). An ISMS is a systematic approach to managing sensitive company information so that it remains secure. It includes people, processes and IT systems by applying a risk management process. While providing goods and services to your customers you come across information about their business. You are under an obligation to protect that information and keep it confidential. Only those persons who are required to process or deal with the information should have access to it. Further, it is your duty to put necessary controls in place to ensure that the safety of the data is not compromised. This standard enables you to do that by laying down the principles that you should follow. 

Some organizations choose to implement the standard in order to benefit from the best practice it contains while others decide they also want to get certified to reassure customers and clients that its recommendations have been followed. In both the cases, your clients will get a valid assurance that the information that they have shared is safe.