The literal meaning of zakat
In defining zakat, it is said to have both the meaning of cleansing and nurturing. If zakat's definition is taken from the root Arabic word, tazkiya meaning cleansing, the sense of zakat becomes attached to property, i.e. cleansing one's property from God's share of the work and others' past efforts, or primary materials and investment.

Zakat in practice
From the perspective that the rights of every manufacturer and worker are equal to his/her current labour, if the zakat on a property or goods is not deducted, one can say it has not been cleansed. In other words it has not been cleansed of other's rightful shares.
Since God's earthly representative is a righteous, Godly administration and the representative of others' historic efforts is indeterminable (innumerable people having participated in the accumulation of investment and invention) the fruits of those endeavors belong to an unknown proprietor, and are therefore at the disposal of the Islamic state. Therefore it is said zakat is payable to the Islamic state.
And since nature (the earth) is all derived from Him (Allah), the administration must use nature's share in manufacturing (zakat) to a benevolent purpose, the benefit of which will be felt by the whole of the Muslim community. In Islam, the government can use force in the collection of zakat. This testifies to the importance attached to zakat in Islamic jurisprudence. In the Holy Qur'an we read: "There is nothing for man but his work." In words each worker and manufacturer must (has the right and responsibility to) subtract the value of their own labour from the gross value of manufactured goods or property, and pay the remainder as zakat , so it may be spent to benefit society. Islam's emphasis upon the establishment of equity and payment (of zakat) is given for this reason.

Zakat as growth
If we calculate the share of historic efforts and God's share from all the goods as zakat and place this at the disposal of the Islamic government to spend on road building, hospitals, universities, etc. then expansion and economic growth will undoubtedly be achieved and poverty eliminated.

Zakat found in all things
On page 273 of the book, "Tohf-al-Hoquq" an oration from, Imam Jafar Sadeq (AS) states, "In the totality of goods and services there is zakat." It means one cannot think of a product in which manufacture, nature and investment have played no part. Therefore, commercial auditors must scrutinize and analyze even the most common of goods or services, and determine the proportion of zakat they contain. Obviously as technology advances, the share belonging to historic efforts (investment) and God's work (nature) will increase, and proportionately the zakat as well. For example, in an airplane, the role of historic work which is the scientific efforts of scholars spread over hundreds of years and the role of inventors and others who have left the world and are no longer present is clearly visible. From another angle, nature has also played a large part. If man wanted to create the earth's environment and atmosphere, he would have to make a supreme effort, the knowledge for which he still does not possess. Since air pressure is a factor in aircraft flight, automatically God's work becomes clearly evident in air transportation and its constituents. Therefore a lot of historic effort has gone into aircraft production, because it has benefited from a high level of technological input and a massive investment of manpower. Zakat is nothing more than the accumulation of the value of God's work and human efforts in history, which must be paid to the government. In today's capitalist system the source of profits must be accepted to stem from the payment of substandard wages (i.e. not compatible with the effort put in) and the withholding of zakat.

The missing link in Marx's added value
Karl Marx became aware of this theory through his friend and colleague Friedrich Engels. Engels had gained knowledge of Arabic and while studying Islamic texts, in particular ibn Khaldoun's (1332-1406) Al-Muqadamah, he came across this theory. This missing link' was a theory which ibn Khaldoun had devised 400 years before Marx, but which Marx misunderstood, and he reshaped with one of its crucial arguments absent from his writing. Marx, according to this theory of the value of labour, says a product is nothing but the culmination of a worker's efforts. If for example using specific technology a society produces a hundred pairs of shoes in a year and for the production of those shoes, it uses one thousand hours of labour (whether the people are lazy or diligent) each pair of shoes takes up ten hours of that society's useful work hours. Thereafter in another theory, called the theory of added value, he (Marx) says the employers divide the workers' earning into two parts. One part he pays to the workers, which Marx calls "paid work," and another part he withholds, which Marx calls "unpaid work." This unpaid work, for labour constitutes the added value or profit, which the employer allots to himself and thereby defrauds the workers of their rights, one could say the employers' places are built on the workers' unpaid wages.
Therefore he encouraged workers to revolt and take back their misappropriated rights from their employers. Marx believed profits were nothing more than the workers' unpaid wages. He therefore concluded with the advanced of the capitalist system, day-by-day, inventions and innovations in machinery would lead to automation and self-operation in that equipment and machinery. This meant workers would lose their jobs and create an army of unemployed. In other words, with the automation (of machinery) employers would lose their source of profits, since in his view, profits were nothing but unpaid workers' wage. Therefore when day-by-day, the number of factory workers is cut back, one could say the employers' profits (wages unpaid to workers) are cut back. This is why Marx elaborated the theory of diminishing returns (profits) in capitalist systems and concluded that the advance of capitalism leads inevitably to its own demise. Since in this system profits are the motor and motive of economic activity, when profit is destroyed (with total automation of machinery, such as with today's robot-run car assembly plants), factories will close and an army of the unemployed will rise against the capitalist system. They will set up a workers' government (dictatorship of the proletariat).
Apart from the errors Marx made in putting forward his theory that added wage is always in decline, it must be considered a false prediction. Instead wherever factories are most automated, profits are seen to increase, rather than diminish. The reason for increased profits must be identified in the lack of zakat payments.
Since the value of a product is equal to the value of three types of work, and the value of current labour is (seen by workers to be) rewarded by the industrialist capitalist at an optimal rate, workers are satisfied to a level which curbs their revolt. Therefore the source of profits must be found in the value of the two other types of work we mentioned earlier- nature and historic investment, which employers unjustifiably allocate to themselves as profits. It is because of this that the more sophisticated machinery becomes the result of the increased share of work contributed by nature and historic investment that the owners of such industries will continue to see their profits rise.

NOTES
1. For a comprehensive description please refer to Ayatollah Sistani's treatise, page 353, the section on the rules of zakat.