The hidden treasure is the true Self or Atman, which is essentially One with God. "Without knowing it" means that the man is not conscious of this Self. Inheriting and selling the field means, reincarnating, reinheriting the body and the physical world of experience. We have three incarnations represented here for purposes of illustration, but of course the actual process takes many more lifetimes. "Plowing" means directing consciousness inward, seeking within oneself. Finding the treasure means finding the Self, becoming consciously aware of the Self within. "Lending with interest" means teaching and spiritual work after attaining Realization.