Charles Ellicott Commentary Exodus 19:23

"And Moses said unto Jehovah, The people cannot come up to mount Sinai: for thou didst charge us, saying, Set bounds about the mount, and sanctify it." — Exodus 19:23 (ASV)

The people cannot come up.—Moses probably means that they cannot do so unwittingly; he does not contemplate the case of an intentional trespass.

But it was this that God knew was contemplated and desired to prevent.