How are "all types of beings originally formless"?
The pull downwards into form, into the unenlightened craving for identity, is driven by craving. Craving leads to grasping and then to rebirth.


  SN12.23:4.6: I say that rebirth has a vital condition.
  
  SN12.23:4.7: And what is it?
  
  SN12.23:4.8: You should say: ‘Continued existence.’
  
  SN12.23:4.9: I say that continued existence has a vital condition.
  
  SN12.23:4.10: And what is it?
  
  SN12.23:4.11: You should say: ‘Grasping.’


In contrast, moving upwards skillfully, we have practice that leads to the formless and beyond:


  SN46.54:15.9: The apex of the heart’s release by equanimity is the dimension of nothingness, I say, for a mendicant who has not penetrated to a higher freedom.”