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 beings 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
 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: Thus is Suffering.
The learner understands, as it really is: Thus is the Cause of Suffering.
The learner understands, as it really is: Thus is the End of Suffering.
The learner understands, as it really is: Thus 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 that!
 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 is the ability to understand refined
in these three aspects... When the Noble friend is thus leaving ignorance all
behind, there is development of the ability to Understand. When the Noble
friend is developing the ability to understand, then ignorance is left behind.
Thus mutual is this enhancement.
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 (Panna-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 folks,
if one searches and asks both slightly, moderately and highly wise teachers,
then the insight of the Buddhas shall come to shine inside the mind!
The Basket of Conduct, Cariyapitaka

More of the 10 mental perfections (paramis):

More on the supreme Understanding Ability:

Understanding is the Chief!