And he said, Certainly I will be with thee; and this shall be a token unto thee, that I have sent thee: When thou hast brought forth the people out of Egypt, ye shall serve God upon this mountain. Certainly I will be with thee - This great event shall not be left to thy wisdom and to thy power; my counsel shall direct thee, and my power shall bring all these mighty things to pass.
And this shall be a token - Literally, And This to thee for a sign, i.e., this miraculous manifestation of the burning bush shall be a proof that I have sent thee; or, My being with thee, to encourage thy heart, strengthen thy hands, and enable thee to work miracles, shall be to thyself and to others the evidence of thy Divine mission.
Ye shall serve God upon this mountain - This was not the sign, but God shows him, that in their return from Egypt they should take this mountain in their way, and should worship him in this place. There may be a prophetic allusion here to the giving of the law on Mount Sinai. As Moses received his commands here, so likewise should the Israelites receive theirs in the same place. After all, the Divine Being seems to testify a partial predilection for this mountain, for reasons that are not expressed. See Clarke's note on Exodus 3:5.