It's organized and meets the requirements, but you should put more of yourself into it. 

Drop the passives, tell a story, explain how you ended up doing engineering instead of medicine, outline the possibility of you achieving this dream or wish  - make it personal and interesting.

In the IELTS Writing Descriptors for Task 2, for Band 7 an "awareness of style" is required under lexical resource – not just knowing the word, but knowing how it is used (see http://www.ielts.org/pdf/UOBDs_WritingT2.pdf). This can mean using simpler words in a more relaxed style – NOT using more complicated words in a very formal style.   

Above all, don't state the obvious. A sentence like this:

From the start of the human society, the necessity of cure for sickness has been significant.

does not really tell us anything new. You already told us that "medicine is of considerable importance in life."  

Vocab and Usage

Medicine is one of my most main interests – or favorite/closest/deepest/chief, etc.

Word Order

In the contemporary life, people more consider their heath.

could change to 

Today, people have become more concerned about their health.

 

The subject helps learners more grasp the body’s organs 

could change to

The subject helps learners to understand [more about] the functions of the body’s organs. 

Word form

The medicine progresses become one of the foremost indices

could change to

• Medical progress is a key index of development  OR
• Advanced medical care is a key indicator of development.

Try to have three, not two examples in a sentence:

It must be fantastic to know how your body composed and how the stomach, the lung work.

could change to

It must be fantastic to know how your body is composed and how the stomach, lungs, and other organs and systems work.

Irregular past tense ('lead', etc)

Leaded by this aim, medicine’s students are encouraged to…

change to 

Led/Inspired/Guided by this aim, medical students [students of medicine] are encouraged to… 

Empty phrases

Try to avoid empty phrases like 'a large number', 'day after day', 'from the beginning of time', 'there is'/'there are': 

Day after day, there is a large number of patients cannot afford to pay their medical services

This could be radically shortened to

Many patients cannot afford treatment.

Verb Tense

I'm not sure about the verb tense in your sentence. Should it be hypothetical (conditional), since you are an engineer and not a doctor at the moment?

Being a voluntary doctor I am able to help poor sick to obtain basic treatment for their ill health.

This could change to 

As a volunteer doctor, I would be able to help the poor and sick to obtain basic treatment.

Usage: Try to use verbs instead of nouns

There are five 'heavy' nouns in this sentence:

From the start of the human society, the necessity of cure for sickness has been significant.

The nouns weigh down the sentence and make it flat and uninteresting. Replace nouns with verbs.  But there is another problem in the sentence  - it doesn't really say anything.  There's nothing wrong with the grammar – it's just a non-dynamic sentence.

What about this?:

We have always needed doctors.

 In the sentence:

Medicine is of considerable importance in life

 Change the nouns to adjectives (and show the reader that you know he or she knows something already):

 Medicine is, obviously, very important.

Simplify: Drop the passives, drop unnecessary nouns, drop all sentences which don't really tell us anything we don't know. 

 Its role has been especially affirmed in epidemic diseases where life of human was threatened.

could change to

Medicine helps fight epidemics like AIDS and flu infections. 

I look forward to seeing essays with more of your opinion in them! Sorry to take advantage of your 'considerable willingness to receive comments'  but I know you can write  - just relax and write! 

There are numerous subjects I have opportunities to study myself or to be taught. Nevertheless, medicine is one of my most interests which I have never learnt. If I had an opportunity I would choose medicine as a discipline to study. This essay covers some main reasons for clarifying my choice.

First of all, medicine is of considerable importance in life. From the start of the human society, the necessity of cure for sickness has been significant. Its role has been especially affirmed in epidemic diseases where life of human was threatened. Moreover, in the contemporary life people more consider their heath. As a result, the medicine progresses become one of the foremost indices of social development.   

Secondly, there are various interests and attractions of studying medicine. The subject helps learners more grasp the body’s organs and their functions. It must be fantastic to know how your body composed and how the stomach, the lung work. On the other hand, one of the most notable aims of medicine is looking for new medical treatments. Leaded by this aim, medicine’s students are encouraged to learn, train and practice their abilities.

Finally, if I could study medicine and become a doctor, I would help the poor in my country. Day after day, there is a large number of patients cannot afford to pay their medical services. The poor, therefore, do not obtain minimum conditions of health care. Being a voluntary doctor I am able to help poor sick to obtain basic treatment for their ill health.

To sum up, although I am an engineer in transportation field, there is a desire to be a voluntary doctor in my mind. It will possibly never come true, but I will support voluntary doctors all over the world as much as I can.

Word count: 296 words

There is considerable willingness to obtain your comments :)