As per the "Bhagwat Gita", at the death of a person this "Jiva (जीव) takes aways all the human senses, its past, present sensory experiences & all the past, present memories with it. It is so subtle that due to its "Immaterial" nature it can travel at the speed of Light & can travel from one planet to another. So due to all the Karmic law as destined by God, it goes from one body to another in the different worlds. So the "Jiva (जीव)" moves from one body to another & one world to another world in "Time & Space", so that's why, It is also called "A Cosmic Traveller"
Below are some verses of "Bhagwat Gita", which clearly tells that there are so many Material Worlds in which a Jiva (जीव) which is a spark of the all pervading Cosmic Consciousness, travels from one place to another after taking repeated births. These are those people who have not yet known the God, hence they take repeated births.
"sariram yad avapnoti
yac chapy utkramatishvarah
vayur gandhan ivasayat" (Bhagwat Gita: Chapter Fifteen verse 8)
"Sri Krishna said: O Arjuna, The living entity (Jiva (जीव)) in the material world carries his different conceptions of life from one body to another as the air carries aromas. Thus he takes one kind of body and again quits it to take another."
"srotram chaksuh sparshanam cha
rasanam ghranam eva cha
adhisthaya manas chayam
visayan upasevate" (Bhagwat Gita: Chapter Fifteen verse 9)
"Sri Krishna said: O Arjuna, The living entity (Jiva (जीव)), thus taking another gross body, obtains a certain type of ear, eye, tongue, nose and sense of touch, which are grouped about the mind. He thus enjoys a particular set of sense objects."
"utkramantam sthitam vapi
bhunjanam va gunanvitam
pasyanti jnana-chaksusah" (Bhagwat Gita: Chapter Fifteen verse 10)
"Sri Krishna said: O Arjuna, The foolish cannot understand how a living entity (Jiva (जीव)) can quit his body, nor can they understand what sort of body he enjoys under the spell of the modes of nature. But one whose eyes are trained in knowledge can see all this."
"yada sattve pravreddhe tu
pralayam yati deh-bhrit
tado Uttam-vidam lokan
malan pratipadhyate " (Bhagwat Gita: Chapter XIV verse 14)
"Sri Krishna said: O Arjuna, "When one, Jiva (जीव) dies after doing Great & Good Karmas & established in the mode of goodness, he attains to the pure higher planets of the great sages."
"rajsi pralayam gatva
tatha pralinas tamsi
mudhh-yonishu jayate" (Bhagwat Gita: Chapter XIV verse 15)
"Sri Krishna said: O Arjuna, "When one, Jiva (जीव) dies after doing Mixed Karmas in the mode of passion, he takes birth among those engaged in fruitive activities; and when one dies in the mode of ignorance, he takes birth in the animal kingdom."
"urdhvam gacchanti sattva-stha
madhye tish-thanti rajasa
adho gacchanti tamasa (Bhagwat Gita: Chapter XIV verse 18)
"Sri Krishna said: O Arjuna, "Those Jiva (जीव) situated in the mode of goodness after doing Good Karma's gradually go upward to the higher planets; those in the mode of passion after doing Mixed Karma's live on the earthly planets; and those in the abominable mode of ignorance after doing Bad Karma's go down to the hellish worlds."
punara vartino ajuna
mam upetya tu kauntey
punara janm na vidhyate" (Bhagwat Gita: Chapter VIII verse 16)
"Sri Krishna said: O Arjuna, "From the highest planet of Brahm Loka in the material world down to the lowest world, all are places of misery wherein a person comes in repeated birth and death from time to .time. But one who attains to to Me (God), O son of Kunti, never takes birth again."
"para's tasmat tu bhavo a'nyo
a'vyakto a'vyaktat sanatanah
ya sa sarveshu bhuteshu
nashyatsu na vinashyati " (Bhagwat Gita: Chapter VIII verse 20)
"Sri Krishna said: O Arjuna, "Beyond the above said material worlds, which are all perishable, there is another unmanifest nature, which is eternal and is transcendental in nature. It is supreme and is never annihilated. When all in this material world is annihilated, that part remains as it is i.e. it is never annihilated & there is eternal life."
Lord Sri Krishna is the Supreme Lord & just like the sun is eternally associated with his rays so the transcendental God Sri Krishna is eternally joined with the “Jivas”. The jivas are the infinitesimally small particles of His spiritual effulgence and are, therefore, not perishable like mundane things. “Jivas”, being part of Divine Lord’s effulgent rays, exhibit on a minute scale the divine qualities of God. So “Jivas” are identical with the qualities of Lord only.
Though Lord Krishna is the all powerful, all-pervading, all-extending Supreme Lord; but Jivas are confined to bodies only. When a Jiva meditates through devotion & merges with the Lord then only he attains to the Lord’s all powerful, all pervasive sublime nature.
Jai Sri Krishna