Exodus 17:6 - Matthew Poole's English Annotations on the Holy Bible

I will stand before thee there, in my cloudy pillar, which shall stand over that place. Horeb and Sinai are sometimes spoken of as the same place, and sometimes as two differing places, as here, compared with Exodus 19:2. The learned write, that this was one long mountain, whereof there were two eminent parts or tops, the one at a considerable distance from the other, and Horeb was the first part of it, and near Rephidim; and Sinai the more remote, to which they came afterwards. Moses did so, i.e. smote the rock, and the waters flowed out plentifully and continually, making a river, which God caused to follow them to their several stations. See 1 Corinthians 10:4.