It was necessary for those who had not accepted Islam...
It was necessary for those who had not accepted Islam, to take a justified tax from them and spend it on their life and safety of their wealth. To protect the life and wealth of people the Islamic government was forced to keep the army on strategic points, which accrued huge expenses. To meet this expense the only way was to acquire money from the people and spend it for their own welfare. Especially when there was war against the enemies, the non-Muslims did not send their men.
We have many historical facts, from which we come to know that this tax, which is generally less was not to put pressure on the non-Muslims, but its purpose was to give peace and for safety measures.
We give some examples for it: When Abadah ibn al-Samit invited the commanders of Egypt towards Islam, he said to them: It depends upon your wish that after studying and pondering accept Islam and if you dont want to become Muslim then give the Jizya (capitation tax) and live under the protection of the Muslim government. Till we are there and you are there, we will behave with you in such a way that each other will be happy.
We promise you that we will protect your lives, wealth, property and land and whoever will cross the border, we will fight against them. When the Muslims were victorious over the Romans and many parts of Shamat came under their control, the people of Hims (in Syria) accepted to pay the Jizya (capitation tax). Afterwards, the Muslims due to some reasons cancelled the treaty, which was signed between them and Christians of Hims after the agreeing of both the sides, cancelled it.
That is why one of the elder Muslims addressed the people of Hims in this way: Whatever we had taken from you, you take it back from us and whatever agreement we had made, make us free from it. The people of Hims answered: We will never separate from you. Your way and style is much better than the Romans. (If you accept) we will fight against the Roman army by joining the Islamic army.
The quantity of Jizya (capitation tax) applied by the Holy Prophet (a.s.) for the Christians of Najran clarify our stand, because it was decided that they will give yearly three thousand Hilla (the price of each Hilla was forty dirhams), to be paid in two installments. Two thousand Hilla in the month of Safar and one thousand Hilla in the month of Rajab. In the same way the Holy Prophet (a.s.) had a treaty with the people of Ezra on the condition that they will pay one hundred Dinars every year.