The objectives of tooth preparation are all except:
Tooth preparation is the mechanical alteration of a defective, injured, or diseased tooth such that placement of restorative material reestablishes normal form (and therefore function) including esthetic corrections, where indicated.
Generally, the objectives of tooth preparation are to

Conserve as much healthy tooth structure as possible.
Remove all defects while simultaneously providing protection  of  the  pulp–dentin  complex.
Form  the  tooth preparation so that, under the forces of mastication, the tooth or the restoration (or both) will not fracture and the restoration will not be displaced, and
Allow for the esthetic placement of a restorative material where indicated.

Reference:  Sturdevant operative dentistry. 7th EDITION, Page No:120
To conserve as much healthy tooth structure as possible
To remove all defects while providing protection  of  the  pulp–dentin  complex
To retain the defective, injured, or diseased  tooth form
To allow for the esthetic placement of a restorative material where indicated