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.