Q. The First and Second Commandments are in the first person (“I”) because God is speaking. Why is the third person (“He”) used thereafter?
A. The change comes in Ex. 20:7. It does not necessarily imply a change in speaker – someone else taking over in place of God – though a famous Midrashic explanation says that the Israelites found (verse 16) that it was too overwhelming for them to hear God’s own voice and they were frightened they would die, so they pleaded with Moses that he should be the Almighty’s spokesman.