Understanding is the 4th Mental Perfection:

Understanding penetrates, illuminates,
and guides right.
Concentration is the proximate cause of
Understanding.
Understanding is the very manifestation of Concentration.
Understanding is the proximate
cause of Equanimity.
Only
understanding comprehends the meaning, and essence.
Understanding purifies
all the other mental perfections:
Energy acquires
right purpose only, when guided by Understanding.
Only fortified by
Understanding, is determination unshakeable.
Only
Understanding can patiently tolerate other being's abuse.
Only
Understanding induces indifference towards gain and loss..
Only Understanding can secure both own and other's welfare...
The Blessed Buddha said:
Just as red sandalwood is
reckoned as the best of all scented woods, even
and exactly so is the ability to
understand reckoned the supreme among all
the 7 mental qualities, that are the links to self-awakening, by
leading to
enlightenment.
SN V
48-55 Indriya-samyutta
And of what kind, friends, is this evaluating ability of
Understanding ?
In this, friends, The Noble
learner is possessed of direct knowledge about
the arising and ceasing of all phenomena, which is a Noble insight, a fully
penetrating and ultimate
understanding, that gradually realizes and leads
to the utter elimination of all Suffering...
The learner (sekha)
understands, as it really is: This is Suffering.
The learner understands, as it really is: This is the Cause of
Suffering.
The learner understands, as it really is: This is the End of
Suffering.
The learner understands, as it really is: This is the Way to end
Suffering.
This, friends, is the discriminating ability of
Understanding ...
SN V 48-10
Indriya-samyutta

Of minor importance, is the loss of family and wealth...
Catastrophic among losses is the loss of
Understanding.
Of minor consequence, is the increase of family and wealth.
Supreme among
all the gains is the increase of comprehension...
Therefore, friends, you
must train yourself to win better understanding!
AN I
14-5
When the Noble friend avoids ignorant persons, but instead cultivates,
frequents, and honors persons who comprehend, teach, and review the
effects
of profound knowledge, then the ability to
understand
is
refined in these 3 aspects...
When a Noble friend is leaving ignorance all behind,
there is development of
Understanding.
When a Noble friend is developing the ability to
understand, then ignorance is left all behind.
Thus mutual is this enhancement of penetrating
comprehension.
The Path of
Discrimination
A learned man, who due to his great
understanding, despises those of little
learning,
is like a blind man walking around with a lamp in his high hand...
Theragatha 1026
Happy indeed are those possessing nothing...
Those who have won
Understanding, clings to nothing.
While those attached to family, friends
and property,
both possessed and obsessed, are as tied to torture...
!
Udana
II 6

What sort of person is released by Understanding (Pañña-Vimutti)
?
Here a person without experiencing all the 8 stages of absorption, anyway
eliminates all mental fermentations completely, after having perceived them
through insight. Such person is said to be released by
Understanding.
Designation of
Human Types 31
Buddha once said:
Just as the great Ocean slopes down
gradually, deepens gradually, inclines
gradually, and not abruptly like an abyss, even so Paharada, is this teaching
and discipline: a gradual training (anupubba-sikkha), a gradual practice
(anupubba-kiriya), and a gradual progress (anupubba-patipada);
One does not suddenly penetrate to this highest
Understanding...
Anguttara Nikāya II
47
Asking Questions logically leads to Understanding:
As a Bhikkhu walking for alms beg from both low, middle, and high
social folks,
if one searches,
and asks both slightly, moderately, and highly wise teachers,
then the
insight of the Buddhas shall come to shine inside
every mind!
The Basket of
Conduct, Cariyapitaka

More
of the 10 mental perfections (paramis):
https://What-Buddha-Said.net/drops/IV/The_Ten_Perfections.htm
More on the supreme Understanding Ability:
https://What-Buddha-Said.net/drops/Freed_by_Knowing.htm
https://What-Buddha-Said.net/drops/IV/The_Chief_Ability.htm
https://What-Buddha-Said.net/library/DPPN/wtb/n_r/pannaa.htm
https://What-Buddha-Said.net/drops/III/Right_Understanding.htm
https://What-Buddha-Said.net/drops/Understanding_is_the_Chief.htm
https://What-Buddha-Said.net/drops/III/Supreme_Understanding.htm
https://What-Buddha-Said.net/drops/III/Revealing_Understanding.htm
https://What-Buddha-Said.net/drops/III/The_Understanding_Ability.htm
https://What-Buddha-Said.net/drops/III/Outstanding_Understanding.htm