Full Idea
The chief importance of the Continuum Hypothesis for Cantor (I believe) was that it would show that the real numbers form a set, and hence that they were encompassed by his theory.
Gist of Idea
For the real numbers to form a set, we need the Continuum Hypothesis to be true
Source
Shaughan Lavine (Understanding the Infinite [1994], IV.2)
Book Reference
Lavine,Shaughan: 'Understanding the Infinite' [Harvard 1994], p.92