People sometimes ask: What is the point of political philosophy? Why struggle with these abstract theories of politics, economics, and ethics? Aren't people driven more by their vested interests than by abstract ideas? So if we want to improve things, shouldn't we focus on changing institutions and incentives, rather than on wrestling with abstract theories? What's in it for us?
Another webpage gives John Maynard Keynes's famous answer. A fuller answer is:
"The views put forward by such writers as Locke, Hegel, and Marx are neither gospels whose eternal truth cannot be challenged except by criminals or lunatics, nor mere quibbles about the meaning of terms like 'State,' 'freedom,' or 'democracy.' They are important simply because they formulate in reasonably clear and intelligible language the political principles which are the basis of the practical policies of statesmen in different kinds of State. In other words, these theories are derived to a considerable extent from acquaintance with the observable characteristics of actual States and their value as well as their limitations depends on recognition of this. It is impossible to understand the points about which the Russians, the Americans, and the British are disputing without a clear idea of the divergent political beliefs on which much of their practical thinking is founded, and it is equally impossible to recognize the character and importance of those beliefs without relating them to the conflicting policies in which they find expression. This should not be taken to mean that economic actions and political institutions depend entirely on beliefs about political freedom. To suggest this would be as foolish as to hold the opposite view, namely that economic factors completely determine political beliefs. The prevailing tendency, however, is to misunderstand and therefore to undervalue the moral sentiments which political theories formulate, and it is desirable that this tendency should be corrected."
--T. D. Weldon, States and Morals: A Study in Political Conflicts (1947), pp. vii-viii
And here is another famous answer:
"If it is objected that all this seems very abstract and remote from daily experience, something too little concerned with the central interests, the happiness and unhappiness and ultimate fate of ordinary men, the answer is that this charge is false. Men cannot live without seeking to describe and explain the universe to themselves. The models they use in doing this must deeply affect their lives, not least when they are unconscious; much of the misery and frustration of men is due to the mechanical or unconscious, as well as deliberate, application of models where they do not work. Who can say how much suffering has been caused by the exuberant use of the organic model in politics, or the comparison of the state to a work of art, and the representation of the dictator as the inspired moulder of human lives, by totalitarian theorists in our own times? Who shall say how much harm and how much good, in previous ages, came of the exaggerated application to social relations of metaphors and models fashioned after the patterns of paternal authority, especially to the relations of rulers of states to their subjects, or of priests to the laity?
"If there is to be any hope of a rational order on earth, or of a just appreciation of the many various interests that divide diverse groups of human beings--knowledge that is indispensable to any attempt to assess their effects, and the patterns of their interplay and its consequences, in order to find viable compromises through which men may continue to live and satisfy their desires without thereby crushing the equally central desires and needs of others--it lies in the bringing to light of these models, social, moral, political, and above all the underlying metaphysical patterns in which they are rooted, with a view to examining whether they are adequate to their task."
--Isaiah Berlin, "The Purpose of Philosophy" (1962)
And a still fuller answer is:
"Self-conscious...man’s conception of himself does not consist only of what he knows about himself or thinks he knows; it consists also of what he aspires to be. Admittedly, he is not what he aspires to be; he is what he is. But the kind of image he has of himself depends largely on what he aspires to be. He does not get his aspirations from the sciences, not even the social sciences; he gets them, directly or indirectly, from practical philosophy, whether or not that philosophy is tied to religion or to metaphysics. He cannot live from hand to mouth, following custom and accepting all current prejudices as they come. He lives in a kind of society which makes him critical and self-critical. To be happy, he must have aspirations, and must also feel that he can live up to them; he must be true to some image of himself. If he wants what he cannot get, or wants incompatible things, or has ambitions that bring him into conflict with other men, he cannot be happy.
"Not everyone is capable of acquiring for himself a coherent practical philosophy. Not everyone feels the need for it…But some there must be who do the systematic thinking which goes to the making of practical philosophies. They are not scientists; their business is not to explain what happens in the world. And they are not philosophers in the rather narrow contemporary sense; their business is not to explain how we use language or how we get knowledge or what exactly it is that we are doing when we pass moral or aesthetic judgements or when we make decisions. They are philosophers in a quite different sense: they try to produce a coherent system of principles and to establish what needs to be done to enable men to live in conformity with them. They do not merely examine and compare the principles, showing where they are incompatible and explaining their consequences; they do not, like honest shopkeepers, display a large variety of goods, describing them all accurately and leaving it to the customer to choose what pleases him best. They produce a hierarchy of principles, and try to explain how men should use them to make their choices. This is how they help to provide them with a practical philosophy…
"The more men live in societies which change quickly, the more mobile they are in those societies, and the more accustomed to the idea that they can, by taking thought, change their social environment to come closer to their ideals, the greater the part of social and political thought in practical philosophy. Its business is to relate a coherent body of principles to government; its business is to tell us what government should do to realize those principles and how it should be organized to do it. Political theory, as distinct from political science, is not fantasy or the parading of prejudices; nor is it an intellectual game. Still less is it linguistic analysis. It is an elaborate, rigorous, difficult, and useful undertaking. It is as much needed as any of the sciences. Its purpose is not to tell us how things happen in the world, inside our minds or outside them; its purpose is to help us decide what to do and how to go about doing it. To achieve that purpose, it must be systematic, self-consistent, and realistic. We learn to cope with the world, not by collecting principles at random, but by acquiring a coherent practical philosophy, which we acquire largely in the process of considering other philosophies of the same kind."
--John Plamenatz, "The Use of Political Theory" (1960)