<p>What was the motivation for having the <code>reintroduce</code> keyword in Delphi?</p>

<p>If you have a child class that contains a function with the same name as a virtual function in the parent class and it is not declared with the override modifier then it is a compile error. Adding the reintroduce modifier in such situations fixes the error, but I have never grasped the reasoning for the compile error.</p>

When the ancestor class also has a method with the same name, and it is not necessarily declared virtual, you would see a compiler warning (as you would hide this method).
In other words: You tell the compiler that you know that you hide the ancestor function and replace it with this new function and do so deliberately.
And why would you do this? If the method is virtual in the parent class, the only reason is to prevent polymorphism. Other then that just override and do not call inherited. But if the parent method is not declared virtual (and you cannot change that, because you do not own the code for example), you can inherit from that class and let people inherit from your class without seeing a compiler warning.