Likutei Sichos – Vol 23 p 33 ff Post Mattan Torah Mitzvos are about and for [the unchanging] G-d also, while the pre Mattan Torah idea, being that it was for us, was flexible and dynamic. Page 33-4.

Likutei Sichos – Vol 23 p 33 ff Differences between the pre and post Mattan Torah. 1) It was given in its entirety to each Jew [all at once], 2) It was commanded and not done by volunteering, 3) Cannot change. The addition of Anochi changed all that. Page 33.