The first two Commandments discuss the belief in One G-d and having no other gods. The Unity of G-d, however, is realized in the material world through the unity of the Jewish people
G-d spoke to the entire Jewish people on Mount Sinai, yet the Ten Commandments are exressed in the singular -- as if G-d is speaking to a single person
The Tenth Commandment is somewhat difficult: most other commandments involve control or regulation of actual physical acts -- this one encroaches on our very thoughts