Exodus 23:21-24

In the context immediately following the making of the covenant, (that is where we are now here in Exodus 23), the cloud is not mentioned with any authority, but the Angel is. The Angel has already been established as being in the cloud, so adding the cloud was not necessary. I think if you will look in your Bible you will see that the translators have capitalized "Angel." This is because they clearly recognized that this Angel in the cloud is divine, and is in fact Jesus Christ, as we will have confirmed in the New Testament.

Now something very significant is added. Israel is told that they do not merely follow the cloud, but they are to obey the voice—the words of the Angel—in the cloud. They are told that if they do obey His voice, blessings will follow. Most specifically, they are commanded not to commit idolatry—that is, conduct that would specifically be a violation of the first four commandments.