Google Apps for Business uses the CardDAV protocol to allow multiple devices to access the same data and update that data set.
In order to synchronize the content stored in your gmail account, with the content stored in your Contacts.app on your Mac, you will need to add the account in System Preferences> Internet Accounts> Click the plus sign in the lower left corner of the windows. Disregard the Google icon and select 'Add Other Account'. Select 'Add a CardDAV Account'.
Enter your full address, enter either your one time password you created specifically for this purpose on Google's website, or if two-factor authentication is disable, your regular password. Server address is google.com. Click create.
Warning: Prior to doing this it is suggested that you export a backup of your entire address book.