Exodus 19:23

‘And Moses said to Yahweh, “The people cannot come up Mount Sinai, for you charged us saying, ‘Set bounds about the Mount and sanctify it'.” '

Moses is still a little naive. He cannot conceive that the people would disobey Yahweh and break through the bounds and enter the sanctified area of the mountain, for Yahweh has forbidden it, and to him that is final, and besides there is the threat of instant death. But Yahweh knows His people better than he.