What makes enantiomers so special? We study enantiomers in detail. But what makes them more important to study than, say, diastereomers? What I'm trying to ask is, enantiomers are simply a type of stereoisomers that can rotate plane polarized light in opposite directions by the same amount. What makes them more important than other stereoisomers?
Enantiomers have different physical arrangement of atoms. This difference plays a crucial role in biology.


  But, why do enantiomers have different biological activities?
  
  Recognition of chiral drugs by specific drug receptors is explained by
  a three-point interaction of the drug with the receptor site, as
  proposed by Easson and Stedman. The difference between the interaction
  of the two enantiomers of a chiral drug with its receptor is
  illustrated below.
  
  
  
  Source: https://www.khanacademy.org/test-prep/mcat/chemical-processes/stereochemistry/a/chiral-drugs