Why is this an issue?

Public fields break the encapsulation principle, in which other code should not be allowed to manipulate the internal state of an object. The class should provide an API to allow state changes in a controlled manner.

This API could be:

• A public property that gets or sets an internal field
• A read-only public property that gets an internal field
• Methods that set the internal field to a predefined value

How to fix it

Use a property to access the internal variable in a controlled way:

type
  TMyType = class(TObject)
  public
    FName: string;
  end;

type
  TMyType = class(TObject)
  private
    FName: string;
  public
    property MyName: string read FName write FName;
  end;

If the state should only be observed, not modified, consider enforcing immutability on the property:

type
  TMyType = class(TObject)
  private
    FName: string;
  public
    property MyName: string read FName write FName;
  end;

type
  TMyType = class(TObject)
  private
    FName: string;
  public
    property MyName: string read FName;
  end;