Now coming to the point of questions—your first question is: "What am I? Is the body itself matter, or spiritual soul, or a combination of both?" Answer: You are eternal servant of Krishna. The body is matter. The spirit soul is different from the body—it is not exactly combination, but it is encagement. Just like if you put oil in the water, the oil does not mix up with the water. Similarly, soul does not mix with the material body; but due to our material consciousness, we are thinking that the movement of this body is movement of the soul. Therefore, when the body is destroyed, we think the soul is destroyed. That is stated in the Bhagavad-gita, that the soul does not die with the destruction of the body. With the destruction of one body, the soul transmigrates to another body, thus the bondage of material existence. Therefore, to train the soul properly to revive his original consciousness, or Krishna Consciousness, is the real purpose of human life.
Then, your second question, "If this body is pure soul, then why it gets engaged with worldly matter?" As explained above, the body is not the soul, it gets engaged with worldly matter due to its vitiated consciousness. Just like some of us are thinking that "I am American," or "I am Indian"—it is due to vitiated consciousness. The real consciousness is that I am eternal servant of Krishna. Or, it is just like a madman who thinks to himself that he is king, he is free to do whatever he likes, and talks nonsense; but a sane man laughs at him.
Our encagement in the matter is just like a madman's activities. When one is treated by the treatment of Krishna Consciousness, he becomes relieved from all these designative engagements. When I feel as American or when I feel as Indian, and act accordingly, that is the cause of all sorts of anxieties and frustrations. Krishna Consciousness means to come to the pure understanding that one is neither American nor Indian, but he is eternal servant of Krishna, and thus engages himself in rendering loving service to the Lord. This is his pure spiritual life.
As long as he does not come to that standard, he is supposed to be materially contaminated. Krishna Consciousness Movement means to engage our sense in the service of the Lord, just opposed to the materialistic way of life wherein the senses are engaged for sense gratification.
Your third question is, "As You have explained in "Two Essays", that as body is covered by shirt and coat, similarly, soul is covered by mind, intelligence, and false ego—if it is so, then who are mind, intelligence and false ego? Who controls them?" The soul controls the mind and intelligence. When he is designated, he controls the mind and intelligence in one way; but when he is free from designation, he controls the mind and intelligence in another way.
In other words, when the soul is designated, for example, as American or Indian, he controls the mind and intelligence in that direction and acts for that particular nation. Similarly, when he is free from the designations and feels himself as the servant of Krishna, he controls his mind and intelligence for that purpose. That is to say, a soul is destined to use his mind and intelligence for rendering service to others because his original position is servant. A servant has to render service to some master, so when he is in designated condition of life, he accepts somebody as master which is Maya.
Maya is illusion. When a soul renders, therefore, service as American or Indian or any other designation, he accepts Maya as his master, because thinking oneself as Indian or American is illusion. Therefore, one's perfect position of life is to render service to Krishna, and for that purpose control the mind and intelligence. So, the conclusion is, in either of his statuses of life, the soul itself is the controller of the mind and intelligence.
Fourth question: "Where does the spiritual life lead us? How should people recognize whether we do take birth in our next life or not?" Answer: Spiritual life leads us to our original constitutional position free from all designations. This is explained in the Bhagavad-gita as brahma-bhutah status. This brahma-bhutah status means free from all anxieties, without any hankering or lamentation. At that stage only, one can think of universal brotherhood. And the next stage is to be engaged in pure Krishna Consciousness, and thus gradually be transferred to the spiritual world where there is eternal life full of bliss and knowledge.
In other words, the spirit soul, when he is fully liberated from material contamination or designation, he no longer transmigrates to another material body after death. He is transferred to the spiritual world for eternal residence in one of the spiritual planets known as Vaikunthas. The abode of Lord Krishna is the highest Vaikuntha planet, known as Goloka Vrindaban.
People must understand intelligently that they are transmigrating from one body to another at every moment. The body is dying at every moment, and the soul is transmigrating to another body at every moment—this is medical fact. The blood corpuscles are changing at every moment and new corpuscles are taking their place. The old order changes, yielding place to the new. This is going on continually. In this way, the soul is transmigrating from baby body to child body, from child body to boy body, from boy body to youth body. So, at the end, when the material of the body does not act very nicely, the soul has to take another material condition of body, giving up the present one.
The body is changing, but the soul is there. Everyone of us can remember our childhood body or past body. That past body is no longer existing; but I am existing now and I existed in the past, and therefore, I must exist in the future in spite of change of body. These things are nicely explained in the Bhagavad-gita, and we should take advantage of this knowledge.
Fifth question: "To achieve the goal of Krishna, should we pass our life through matter to spiritual life or direct to spiritual life?" The goal of Krishna can be achieved in a second if we simply accept the truth that we are eternal servant of Krishna. Although I am within this material body, I can immediately stop its material function simply by developing my Krishna Consciousness, which means to accept that I am eternal servant of Krishna.
Unfortunately, all the Karmis, Jnanis, and Yogis are thinking of themselves in different degrees that they are not servants of Krishna. Therefore, it is stated in the Bhagavad-gita that after many, many births of different activities under different concepts of life, when actually one becomes wise, he surrenders unto Krishna, understanding Vasudeva Lord Krishna is the Cause of all causes. But such great soul, accepting Krishna as the Supreme Master is very, very rarely to be found.
Fortunately, by the grace of Lord Caitanya, this Krishna Consciousness revival is made very easy, simply by chanting the Hare Krishna Mantra. Therefore, I advise you to chant this sublime Mantra—Hare Krishna Hare Krishna Krishna Krishna Hare Hare Hare Rama Hare Rama Rama Rama Hare Hare, and be happy in this life without any frustrations, anxieties, worries, etc. as you have mentioned in the first part of your letter. This is practical and very easy to perform. Try it sincerely, and your life will be sublime.