Let's first understand something about this body of ours. Our body is made of nature's five gross elements which are Earth, Fire, Water, Air & Ether. There are other subtle elements of nature called Mind (including the senses), Ego & Intellect. Our human body is made up of five above mentioned Gross elements & other subtle elements of nature. Our true nature is that we are the "Immortal Soul" who sits within this nature born body. This Soul is different from this body of ours. Now the difference is only in the perception & belief of ours, whether we consider our self to be this "Body" or the "Soul" within this body. If we believe our self to be a "Body" then we shall die one day as death of a body is certain. But if we believe our self to be a "Soul" then death of an Immortal thing is not possible. So just have a firm belief that you are that Immortal Soul. Then there shall be no death for you & then you shall live even after the death of this body. Below is what the Bhagwat Gita says about this aspect.
As per 'Bhagwat Gita', one who is born, shall die one day & whosoever shall die, shall be reborn again certainly, though the embodied Soul in this body is Immortal. As per 'Bhagwat Gita-Chapter Two Verse - 23', Immortal Soul cannot be cut with any weapon, fire cannot burn it, it is impervious to water & it cannot drench it & neither air can dry this Soul. As Soul is beyond this visible nature elements of Fire, Water, Air, Earth etc. so these nature elements cannot cause any damage to the Immortal Soul.
"nainam chindanti shastrani
nainam dahati pavakah
na chainam kledayanty apo
na sosayati marutah" (Bhagwat Gita: Chapter Two verse 23)
"Sri Krishna said to Arjuna: The Soul can never be cut to pieces by any weapon, can never be burned by fire, can never be moistened by water & can never be dried by the wind."
"acchedyo ’yam adahyo ’yam
akledyo ’sosya eva cha
nityah sarva-gatah sthanur
achalo ’yam sanatanah" (Bhagwat Gita: Chapter Two verse 24)
"Sri Krishna said to Arjuna: This individual Soul is unbreakable and insoluble, and can be neither burned nor dried. The Soul is everlasting, present everywhere, unchangeable, immovable and eternally the same."
If a person becomes firm in that belief only that Soul inside his body is Immortal, then too he attains immortality as then that person goes beyond the visible nature elements which has formed this visible body of ours.
Now what is immortality? This Soul of ours wears this body made of nature elements. After karmic cycle, depending on the Karmas of our previous life, Soul drops this body at death & takes on another body based on the Karmas of our present life. Again we do Karmas in our next birth & that becomes the basis of our further next birth for this Soul. So this cycle of wearing different bodies goes on for this Soul.
We all feel pleasure & pain in one's life, so can't it be possible that we can avoid this pain that we feel in our body. As per 'Bhagwat Gita-Chapter Eighteen Verse - 55', when we go to a perpetual divine life, which is beyond this nature, which forms this body then that life is beyond all this pain & is a blissful life. To attain that we have to establish our self in our Soul. For that we need to have a firm faith that we are that Immortal Soul & not this perishable body. As God is the Supreme Soul from whom all these Souls have emanated, so worshipping him constantly & believing oneself to be a part of that immortal Soul, one shall attain to a blissful life which is beyond the pain & suffering.
"bhaktya mam abhijanati
yavan yas chasmi tattvatah
tato mam tattvato jnatva
visate tad-anantaram" (Bhagwat Gita: Chapter Eighteen verse 55)
"Sri Krishna said: O Arjuna, One can understand Me as I am, as the Supreme Personality of Godhead, only by devotional service. And when one is in full consciousness of Me by such devotion, he can enter into the Kingdom of God."
"sarva-karmany api sada
sasvatam padam avyayam" (Bhagwat Gita: Chapter Eighteen verse 56)
"Sri Krishna said: O Arjuna, Though engaged in all kinds of activities, My pure devotee, under My protection, reaches the Eternal and Imperishable abode by My grace."
So let's change our thinking & have belief that we are that Immortal Soul & not this perishable body. Once we do that then we shall be free from the cycle of birth & death & then we shall become immortal. Then we shall live permanently on a Godly planet where there is no death & life is permanent. When we believe in our Soul nature then we shall have belief in that Supreme God also who is the Lord of all the Souls. He is also called the Super Soul having all the almighty powers & Infinite Bliss. Let's pray to that Super Soul who shall bestow us with Immortality & Supreme Bliss.
Jai Sri Krishna