Adding "ness" to word endings is a type of Hebraism
When we translate words from Hebrew to English, sometimes we need to add "-ness" to make them easier to understand.
Hebrew has different ways of talking about things like kindness or mercy than we do in English.
So, by adding "-ness" to certain words, conveys these ideas in a way that makes sense to English speakers.
The reason we do this is because Hebrew and English are different languages with their own expression.
In Hebrew, they might use special word forms or sounds to talk about feelings or ideas. But in English, we often add "-ness" to make it clear we're talking about a big idea or feeling.
For example, in Hebrew, the word "חֶסֶד" (chesed) means something like "loving-kindness" or "mercy."
But in English, we might add "-ness" to words like "kind" or "merciful" to make "loving-kindness" or "mercifulness."
This way, English speakers can understand the same important ideas that Hebrew speakers do, even if we use different words to talk about them.
1 Nephi 3:216
Either to the convincing of them unto peace and
life eternal,
Or unto the deliverance of them to the hardness of their hearts
And the blindness of their minds,
Unto their being brought down into captivity and also unto destruction,
Both temporally and spiritually,
According
to the captivity of the devil of which I have spoken.'"
(LDS: 1 Nephi 14:7)
Jarom
1:6
Behold, it is expedient that much should be done
among this people.
Because of the hardness of their hearts,
And the deafness of their ears,
And the blindness of their minds,
And the
stiffness of their necks;
(LDS: Jarom 1:3)
Alma
9:67
And thus they having been called to this holy
calling on account of their faith –
While others would reject the Spirit of God on account of the hardness of their hearts and blindness of their minds,
While, if it had not been for this,
They might
have had as great privilege as their brethren;
(LDS: Alma 13:4)
Alma
14:107
Do ye suppose that ye can convince the Lamanites
of the incorrectness of the traditions of their fathers, as stiff-necked
a people as they are?
Whose hearts delighteth in the shedding of blood?
Whose days have been spent in the grossest iniquity?
Whose
ways have been the ways of a transgressor from the beginning?'
(LDS: Alma 26:24)
Helaman
5:100
"And now because of their steadfastness
–
When they do believe in that thing which they do believe –
For because of their firmness when they are once enlightened,
Behold, the lord shall bless them and prolong their days,
Notwithstanding
their iniquity;
(LDS: Helaman 15:10)
3
Nephi 3:57
Therefore, being grieved for the hardness
of their hearts and the blindness of their minds.
Went
forth among them in that same year and began to testify boldly repentance and
remission of sins through faith on the Lord Jesus Christ.
(LDS: 3 Nephi 7:16)
Ether
1:111
Behold, when ye shall rend that veil of unbelief
which doth cause you to remain in your awful state of wickedness and hardness
of heart and blindness of mind,
Then
shall the great and marvelous things which have been hid up from the foundation
of the world from you …
(LDS: Ether 4:15)
Ether
6:92
But behold, the Spirit of the Lord had ceased
striving with them
And Satan had full power over the hearts of the people,
For they were given up unto the hardness of their hearts and the blindness of their minds that they might be destroyed;
Wherefore,
they went again to battle.
(LDS: Ether 15:19)