It is an act of economy to build up the strength of society. Since our wealth is accumulated by the help of others, every one should consider a day for himself as the beginning of his calendar year and upon that day, if he has extra saved after his expenditures, then from his savings he should share one-fifth with the needy. You are not asked how much you made, but you are asked for one-fifth of what you did not use.

The Quran orders us in Sura 8, Aya 41: " And know ye (O believers) that whatever of a thing you acquire, a fifth of it is for Allah, and for the Apostle and for the Apostle's near relatives and the orphans and the needy and the wayfarer, if you are a believer in Allah."

"..eat and drink but waste not by excess, for Allah loves not those who waste."Quran, Sura 7, Aya 31.

In an Islamic environment we make money, we spend it as the Quran states, eat and drink but we do not exceeding and wasting, the extra money left is subject to Khoms.
The Quran gives the good news to those who struggle with their wealth and then their soul in exchange for Heaven.

"Allah has purchased of the Believers, their persons and their wealth; for theirs (in return) is the Garden (of paradise)." Quran, Sura 9, Aya 111.

It also serves as a means of justice in the economic system in that it fills up the gaps in the society or the sharing of wealth is the economic need for Islamic activities and fulfillment of the needy.

Our beloved prophet (PBUH) said: "In wealth there is a due there than Zaka"Nahjul-Fasaha 870

NOTE:Ghanimat (acquire) actually means "profit obtained" which includes the property surrendered by the enemies of Islam, in any battle (i.e. booty). But Ghanimat mentioned here comprises of the profit obtained. Ghanaem means war profit or any profit from material life or business.