'Hard' in the Bible

Be not hard of heart, as when you made me angry, on the day of testing in the waste land,

But give comfort to one another every day as long as it is still Today; so that no one among you may be made hard by the deceit of sin:

As it is said, Today if you will let his voice come to your ears, be not hard of heart, as when you made him angry.

After a long time, again naming a certain day, he says in David, Today (as he had said before), Today if you will let his voice come to your ears, be not hard of heart,

Of whom we have much to say which it is hard to make clear, because you are slow of hearing.

For the order which said, If the mountain is touched even by a beast, the beast is to be stoned, seemed hard to them;