Ezekiel 3:8,9

“Behold I have made your face hard against their faces, and your forehead hard against their foreheads. I have made you forehead as an adamant, harder than flint. Do not be afraid of them, nor be dismayed at their looks, for they are a rebellious house.”

There is a play on words here for the words for ‘hard' and ‘harder' come from the same verbal root as ‘Ezekiel' (‘God hardens'). God will enable him to stand firm and resist all attempts to silence him. The word translated ‘adamant' means literally a thorn bush, but then something pointed and hard (a diamond for engraving - Jeremiah 17:1). Thus here it indicates something hard, ‘harder than flint'. Thus he need not be afraid of them, or be distraught at the looks they give him. And he must indeed expect it because they are rebels against God, Who is the head of their household.