Contradiction with Exodus 19:12
This verse contradicts Hebrews 12:18 by indicating a physical boundary and tangible experience at Mount Sinai, which Hebrews 12:18 states is not the kind of mountain approached in the faith symbol.
Exodus 19:12: And thou shalt set bounds unto the people round about, saying, Take heed to yourselves, [that ye] go [not] up into the mount, or touch the border of it: whosoever toucheth the mount shall be surely put to death:
Contradiction with Deuteronomy 4:11
Deuteronomy describes Israel approaching a tangible, fiery mountain at Horeb, contrasting Hebrews 12:18's claim of not approaching such a mountain in the new covenant context.
Deuteronomy 4:11: And ye came near and stood under the mountain; and the mountain burned with fire unto the midst of heaven, with darkness, clouds, and thick darkness. [midst: Heb. heart]
Contradiction with Exodus 20:18
Exodus recounts the people witnessing tangible physical phenomena at Mount Sinai, contrasting with the spiritual approach depicted in Hebrews 12:18.
Exodus 20:18: And all the people saw the thunderings, and the lightnings, and the noise of the trumpet, and the mountain smoking: and when the people saw [it], they removed, and stood afar off.
Contradiction with Exodus 19:18
This verse describes a very physical and mighty phenomenon occurring on Mount Sinai, in contrast to the spiritual and non-physical mount described in Hebrews 12:18.
Exodus 19:18: And mount Sinai was altogether on a smoke, because the LORD descended upon it in fire: and the smoke thereof ascended as the smoke of a furnace, and the whole mount quaked greatly.