In this description regarding positive theory and normative theory, from what I understand, positive theory is based on fact and cannot be approved or disapproved (e.g., explain how the economy actually operates), and "normative theory" is about the goal at which economies should aim.

From this document, they said:

For example, in the model of the perfectly competitive market, a positive theory played a key role in discussions of how antitrust law could achieve the normative goals of welfare economics. More generally, positive theories are said to show us the means to the public policy ends that normative theorists advance.

I have some questions as below:

1> Why does the author mention "perfectly competition market" in the first sentence? Whether the first sentence says that we need to based on what is really happening to plan for the strategy to achieve the goal?

2> Is the first sentence is explained as above, I do not understand what does the second sentence mean, it seems not link to the first sentence.