'Harder' in the Bible

An offended brother is harder to reachthan a fortified city,and quarrels are like the bars of a fortress.

Lord, don’t Your eyes look for faithfulness?You have struck them, but they felt no pain.You finished them off,but they refused to accept discipline.They made their faces harder than rock,and they refused to return.

I have made your forehead like a diamond, harder than flint. Don’t be afraid of them or discouraged by the look on their faces, even though they are a rebellious house.”