Krsna personally never leaves Goloka Vrindavana as His original two armed form. He is simply enjoying loving reciprocal relations with the Brijwasis devotees.

Krsna personally never leaves Goloka Vrindavana as that original two armed form, so He has nothing to do with the material existence. 

Krsna is Rasabihari, He is simply enjoying loving relations with the Brijwasis associates in Goloka Vrindavana.

Krsna the Supreme Personality of Godhead and cause of all causes, first expands as His older brother Balarama.

Balarama then eventually expands as Visnu (Narayana) who lives on all the Vaikuntha Planets, with each having their own unique name that describes their particular pastime.

However, these Visnu-tattva forms of God on all the Vaikuntha Planets, also have nothing to do with the material existence, Lord Visnu is simply enjoying with the goddess of fortune and all of His other servants. 

As explained, Krsna first expands as His older brother Balarama who facilitates all the beautiful loving reciprocal relationships on the Vaikuntha Planets.

Balarama technically expands Himself first as the quadruple expansions of -

Vasudeva, 

Anniruddha, 

Pradyumna,

Shankarshan. 

Shankarshan and Vasudeva expand themselves as Narayana (Visnu) and Ananta Sesha.

Then Shankarshan expands Himself as Maha Visnu who creates the material creation. 

Maha Visnu is the original source of all material existence that originates from Him. 

Karanadakasayi Visnu is also another name for Maha Vishnu who lays down in the causal ocean within 1/4 of the Spiritual Sky and creates the temporary material energy. 

And where does the causal ocean come from?

It is an ocean created by Maha Visnu's own perspiration. 

While laying in the causal ocean, Maha Visnu exhales uncountable innumerable universes (Brahmandas) that emanate from His breathing and the pores of His Skin.

And all the Brahmanda universes float in the causal ocean.

Maha Visnu is the origin of everything in material creation, it is in His dreaming, while He sleeps, He creates all the material Worlds (Brahmanda universes). 

In all paintings Maha Visnu is seen sleeping and dreaming.

Srila Prabhupada – “This material creation is the spirit soul’s dream. Actually all existence in the material world is a dream of Maha-Visnu, as the Brahma-Samhita describes–

“This material world is created by the dreaming of Maha-Visnu. The real, factual platform is the spiritual world, but when the spirit soul wants to imitate the Supreme Personality of Godhead, he is put into this dreamland of material creation”. (Srimad Bhagavatam Canto 4 Chapter 29 Text 83)

Srila Prabhupada - “Everything happening within time, which consists of past, present and future, is merely a dream. This is the secret in understanding in all the Vedic literature.” (Srimad Bhagavatam Canto 4 Chapter 29 Text 2b)

Srila Prabhupada - "Factually all of material existence is only a dream. Thus there is no question of past, present or future. Persons who are addicted to karma-kanda-vicara, which means ‘working for future happiness through fruitive activities’, are also dreaming. Similarly, past happiness and present happiness are merely dreams" (Srimad Bhagavatam 4.29.2b)

The entire material creation are the dreams of the sleeping Maha Visnu.

As explained, deep inside each massive Brahmanda universe coming from Maha Visnu, is a secondary universe where Maha Visnu expands as Garbhodakashayi Visnu.

Maha Visnu personally expands Himself and enters deep into each of the massive Brahmanda universes into a tiny "secondary universe" within each Brahmanda greater universe

So we can understand how little and small we are in our single universe.

We think this single material universe we are in, deep inside our Brahmanda, is very big, but on the grand scale, our single universe is tiny, very small.

So Maha Visnu enters into each of these little universes and expands Himself as Garbhodakashayi VishLnu.

In other words, Maha Visnu, after creating each Brahmanda universe and their inner secondary tiny universe, then enters as Garbhodakashayi Visnu into each secondary tiny universes.

From Him, Lord Brahma then appears. 

Maha Visnu, through His eyes also glances at each secondary universe within each Brahmanda. 

And from His glance, He impregnates all of the jiva-tattva souls who have chosen to enter the material creation.

Technically, no jiva-souls originates from Maha Visnu, they simple take shelter of Him after choosing to leave the Spiritual Worlds so they can eventually be given access to the material creation via Maha Visnu.

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They then take birth according to their independent rebellious desires that caused them to leave the Spiritual World in the first place to enter a particular material universe and material bodily vessel that matches and suites the desires they have. 

Also it should be clearly understood that the word Earth can also mean "Brahmanda universe" as well as its "secondary inner material universe" that is deep inside the Brahmanda.

Maha Vishnu is like the father who impregnates the mother, meaning Brahmandas that are also called Words or Earth with His glance, then the jiva souls are all born into the material creation from that interaction. 

Garbhodakashayi Vishnu is laying down deep within the secondary universe inside the surrounding Brahmanda.

From Garbhodakashayi Vishnu a Lotus flower sprouts from His naval and upon that lotus flower the original living created being of each material universe Lord Brahma is born. 

Lord Brahma is given the instruction to perform Tapasya and through Tapasya and devotion to the Lord (Maha Vishnu) he has given Darshan of the Supreme Lord and the Lord reveals from within his heart the Vedic knowledge. 

Brahma is therefore the first spiritual master of each universe.

The ultimate purpose of this material creation is to send all jiva souls back home back to Godhead from where they originated. 

Krishna from whom Maha Vishnu has originally expanded from, says at the beginning of the material creation, that I have given the Vedic knowledge through Brahma and then after the Vedas are revealed Brahma begins the process of creation of all the planetary Systems and all the various species of life. 

And of all the species of life, Krishna is to be known as the purpose of creation. 

There are four Yugas, and according to the particular persons desires and  karmic condition that are coming from a previous creation to a new material creation. 

Satya-Yuga is for the very pious where practically everyone goes back to Godhead because they have such an inclination towards spiritual life.

In Treta-Yuga people become slightly become more degraded.

And in Dwapara-Yuga half the population is God consciousness and half are degraded. 

And for those living entities (jiva souls) who have the worst possible Karma, they take birth in Kali-Yuga.

Kali-Yuga is an ocean of faults; it’s the age of Quarrel, the age of hypocrisy, the iron age of irreligion. The age where religion become irreligion and irreligion becomes religion.

However, it is explain in Srimad Bhagvatam that Kali-Yuga is most blessed and most worshipable of all because in the age of Kali the Supreme Lord incarnate in His most munificent and merciful of all incarnation to give everyone love of through the chanting of the holy names 

Hare Krishna Hare Krishna, Krishna, Krishna Hare Hare/Hare Rama Hare Rama, Rama, Rama Hare, Hare. 

Exactly how does this comes about? 

The Lord appears in this age of Kali Yuga as Lord Caitanya to deliver this pure gift of Krishna  indiscriminately to everyone not considering qualification or disqualification.