This is the Socialist Party message

The capitalists try to present their system as the best of all possible worlds.  The system is built so the capitalist can be free to enslave and exploit us. The capitalist class says revolution was good in the past when they were making it, to give themselves the political power to bring about their system. But then they want it to stop. But now things have reached a new stage where for the first time in history the working class, which represents the majority of society, is not only going to do the fighting but is also going to take the benefits and use them for the majority of society and for mankind as a whole.  From 1904 until to-day the Socialist Party has delivered the same message day after day, week after week, month after month, year after year and still the workers let themselves be led up the blind alleys of disappointment and despair, following leaders with pathetic trust on the painful march to a promised land that always remains over the hill.

Is the Socialist Party message so hard to understand? No! It is the very essence of simplicity. The workers produce the wealth of the world, the capitalists own it. Just as the workers hand over what they produce to-day to the capitalists, they could keep it for themselves if they wished to do so. The capitalists perform no useful task in wealth production, they are just parasites. They take the fruits of the workers' labour because the workers let them, and the workers let them do so because they are duped by the myth that the capitalists are necessary. The aim of the capitalists is to force or cajole the workers into the submissive attitude of willing slaves, heaping up wealth for others to enjoy, and flattery and promises, cant and hypocrisy will be instruments used to secure this end. It is not remedies for particular social diseases that we need but the removal of the source of all social disease—the legal figment that enables the capitalists to live on our backs. The legal arrangement that because a man has money he, therefore, has the right to exploit his fellow men is a social agreement that has not always existed, and it can be abolished at any time that society decides to take this step. Society includes everybody, both workers and capitalists, and the workers are the great majority in society. The workers of the world can control their destinies once they shed their delusions and cast off the useless burden of capitalist privilege that they have borne upon their backs for so long. But the work they have to do must be done by themselves.  The only path is knowledge of what we are, wealth-producing slaves of capital, and what we can be, freely associated workers owning in common our means of production and using them to supply the needs of all, without the intervention of privilege of any kind except youth, age or sickness

The history of mankind can be described as the history of the efforts of human communities to free themselves from the constraints always imposed by the necessity of meeting their daily survival needs and reproducing the species.  This statement sums up historical materialism. The purpose of socialist revolution is not to restore a “natural order of things” that was somehow got rid of at some point in history. The various forms of society in the past have been the responses worked out by men and women to surmount the problems of how to survive and reproduce. Chattel slavery was just as “natural” a practice as is capitalist exploitation today. The purpose of socialist revolution is to provide today’s society with a form of organisation that corresponds to the material possibilities open to us today and that satisfies the current conditions that the history of mankind has taught us to consider most appropriate to the well-being of humanity. Contemporary society has the objective material capacities – in the developed societies, at any rate – to put an end to capitalist exploitation and all the forms of oppression that it perpetuates. This is the basic and primary reason for working for socialism.

Marxism holds that the life of human society is in the final analysis determined by the level of development of the productive forces. It can be described as the first rigorously study and scientific vision of society. Marxism does not hold that the existence and development of societies are determined absolutely, that they have no freedom? If it did then it is misleading to hold out the prospect of revolution, for in the final analysis it would be the determinism of the productive forces that counts. Men and women can make plans for their individual and collective existence. The development of societies does not follow a predestined, predetermined course. Societies can act on and influence their development.