Krishna arranges everything in this material world in the most wonderful manner that it reflects the spiritual world but at the same time accommodates people who are not in the consciousness of the spiritual world. So people with similar mentalities and proclivities are placed in similar situations (in a varnasrama society).
Lecture on SB 3.6.32 – About the Four Varnas – Vyasa Puja 2008 – 5th Jan'08 – Tirupati
Everyone sees the world in a different way according to his mentality. If a brahminically inclined person goes to a forest he will think, "This is a nice place to sit and chant Hare Krishna and meditate on Krishna." If a ksatriya goes, he will think, "We have to go on hunting, killing the wild animals who are disturbing the rsis." If a vaisya goes he thinks how to purchase the forest, sell the timber, make profit, then clear the land, make the condominium." If a sudra goes, he will think, "I will bring my girlfriend here and we will enjoy." And if a devotee goes, he sees Krishna.
Lecture on SB 3.6.32 – About the Four Varnas – Vyasa Puja 2008 – 5th Jan'08 – Tirupati
In Treta Yuga, organization of society was required, because people had more material desires. Not everyone was committed directly to full spiritual involvement, and therefore it was required that there be some production. They required some more opulent food stuffs; then they have to be produced and gold and jewels—these things were available but some endeavor was required to bring them out. So then society needs organization. Then varnasrama began: brahmanas, ksatriyas, vaisyas, sudras, each with their specific mentality.
Lecture on SB 3.6.32 – About the Four Varnas – Vyasa Puja 2008 – 5th Jan'08 – Tirupati
In Satya-yuga there was no need of any organization because people were content to live very simply. They were all hamsa-jati. They were all very spiritually advanced and were prepared to live on whatever leaves and roots and fruits were available.
Lecture on SB 3.6.32 – About the Four Varnas – Vyasa Puja 2008 – 5th Jan'08 – Tirupati