Full Idea
On the bundle theory, the identity of indiscernibles (for 'individuals') is a necessary truth, since an individual is just the co-instantiation of all the properties represented by a point in the space of properties.
Clarification
The bundle theory says an object is just a bundle of qualities
Gist of Idea
The bundle theory makes the identity of indiscernibles a necessity, since the thing is the properties
Source
Robert C. Stalnaker (Mere Possibilities [2012], 3.6)
Book Reference
Stalnaker,Robert C.: 'Mere Possibilities' [Princeton 2012], p.71
A Reaction
So much the worse for the bundle theory, I presume. Leibniz did not, I think, hold a bundle theory, but his belief in the identity of indiscernibles seems to have had a theologicial underpinning.