The reasons for the expulsion of souls from the spiritual world.
It was because she became envious of God, wanted to know and taste the same pleasures as Him, challenged His authority, refused to serve Him with devotion, and thus distanced herself from Lord Krishna, that the beautiful, pure soul who lived with God was expelled from the spiritual world. All this is the cause of the estrangement of the fallen souls from God, and their imprisonment in the matter of the material universe.
All beings were created together, simultaneously.
Contrary to a widespread misconception, during Creation, God created all 8,400,000 living species—human, animal, and plant—at the same time, simultaneously. True evolution does not occur at the level of the physical envelope, but at the level of consciousness.
Therefore, if a spiritual being incarnates within a lower species, animal or even plant, they must gradually evolve to higher species, human or even celestial.
Of these two energies: life and matter, or life and the soul, the latter represents the higher, original energy. As for matter, which is the lower energy, it comes from life. They exist simultaneously.
For the well-being and harmony of all spiritual beings who were to live in the material universe, God gave them all a body according to each person's karma. Their respective bodies were all created by Krishna, the Supreme Personality of Godhead, together, at the same time, simultaneously.
The reasons for the soul's imprisonment in matter.
The spirit souls who descended into the material universe themselves made this choice.
The Lord said: If the soul finds itself thus imprisoned, it is because it harbors a false conception of its identity and considers itself the supreme beneficiary. It is this false ego in the living being that forces it to experience incarceration within material existence. As the Supreme and Absolute Truth, I personally stand beyond the living being, as well as its material envelope. Both energies, material and spiritual, act under my sovereign authority.
The spiritual being is separated from Krishna, the Supreme Personality of Godhead, because of his disobedience to the Lord, his refusal to serve Him with love and devotion, his envy of Godhead, and his questioning of the authority and supremacy of the Supreme Personality of Godhead; his true meaning is therefore lost.