Calm
(samatha) and Insight
(vipassanA):

There are two principal kinds of mental development
(bhāvanā):
1: Development of mental
tranquillity and
calm
(samatha-bhāvanā)
culminating in the development of
concentration
(samādhi-bhāvanā)
And!
2: Development of
insight
(vipassanā-bhāvanā)
culminating in the
development of
understanding
(paññā-bhāvanā).
Both qualities:
Calm and
Insight, are essential
and crucial for release!
Tranquil Calm
(samatha) is the pleasant, peaceful, yet lucid state of
a settled mind acquired as a preliminary to meditative absorption.
It blesses the meditator
with 3 things: Happy life, happy rebirth, and
a
mental purity suitable for gaining progressively
penetrating insight..
Concentration is a necessary prerequisite for such incisive insight..
Why so? It removes
the distractions that veil the investigating vision!
Insight is that, which leads to entrance of the
4 stages of Nobility..
Why so? It irreversibly removes gross and
latent
mental hindrances!
The term
samādhi literally means ~being firmly put evenly together
(sam + a + dha), and is mental state focused on only one
single object:
cittassa-ekaggatā,
which literally means ~ mind gone one place only =
one-pointedness of mind.
Any state of consciousness has a degree of mental concentration!
One may distinguish these four
increasing levels of concentration:
1: Momentary or transient
concentration
(khanika-samādhi),
2: Preliminary or preparing
concentration
(parikamma-samādhi),
3: Access, approach,
or neighborhood
concentration
(upacāra-samādhi),
4: Absorption, or attainment
concentration
(appanā-samādhi).
Insight
(vipassanā) is the penetrative
understanding, gained by only
direct meditative experience of the inherent
transience,
misery,
and
selflessness
(anicca,
dukkha, anattā) of all physical and mental states
of being included in these
5 clusters
(khandha) of
mental clinging:
form, feeling, perception, mental construction, and consciousness...
Bhāvanā
is derived from the causative form of the verbal root
bhu,
bhavati
=
to be, to become, causing to be, making come into being,
the calling into existence of, the production of, or development of.
When applied to Mental Training this simply means
Meditation...

Simultaneous
Calm and
Insight!
More
on Insight (Vipassanā):
https://What-Buddha-Said.net/drops/II/Highway_to_Nibbana.htm
https://What-Buddha-Said.net/drops/II/The_18_Principal_Insights.htm
https://What-Buddha-Said.net/drops/IV/Breathing_Calm_and_Insight.htm
More on Calm (Samatha):
Forest
Bliss, Calm, Calm_and_Insight, Calm_Power, The_Tranquil_One,
Breathing_Calm_and_Insight, Silenced, Forest_Bliss2, Calmed...
:-)