Why are the words "mano" & "manasa" used in the opening Dhammapada verses?

There are not many responses to this question therefore I will provide my view.

1. The term 'mano' is used primarily in the suttas to refer to the mind as a sense organ. The sense organ of the mind not only knows the mind's feelings, perceptions & thoughts but also knows Truth (such as cause & effect, impermanence, unsatisfactoriness & not-self) and even Nibbana. Therefore, it is 'mano' as a sense organ that perceives Truth and thus develops knowledge & wisdom (or otherwise, remains ignorant or instinctual). Thus, mano, having been translated as 'the intellect', is that which makes decisions and develops intentions.

2. Related to the word 'mano' is 'manasa'. Manasa is one of the three types of kamma, namely:

It is intention that I call deeds.

Cetanāhaṃ, bhikkhave, kammaṃ vadāmi.

For after making a choice one acts

Cetayitvā kammaṃ karoti—

by way of body, speech and mind.

kāyena vācāya manasā.

AN 6.63

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In the same way, deeds of body, speech and mind should be done only after repeated checking.

Evameva kho, rāhula, paccavekkhitvā paccavekkhitvā kāyena kammaṃ kattabbaṃ, paccavekkhitvā paccavekkhitvā vācāya kammaṃ kattabbaṃ, paccavekkhitvā paccavekkhitvā manasā kammaṃ kattabbaṃ.

MN 61

3. In addition, the words 'manosaṅkhāraṃ' ('formation of/by mind') & 'manosañcetanāhetu' ('mental intention as a cause') are often found exclusively in suttas about intention & kamma (eg. AN 3.23; AN 4.171; SN 12.25).

4. Therefore, it appears obvious by both the words 'mano' & 'manasa' and the contextual teaching found in Dhammapada 1 & 2 about "a person speaks or acts" that Dhammapada 1 & 2 are about 'kamma' rather than about a 'solipsistic' or Brahmanic creationist princple. Dhp 1 & 2 say:

1. Mind precedes all dhammā. Mind is their chief; they are all mind-wrought. If with an impure mind a person speaks or acts suffering follows him like the wheel that follows the foot of the ox.

2. Mind precedes all dhammā. Mind is their chief; they are all mind-wrought. If with a pure mind a person speaks or acts happiness follows him like his never-departing shadow.

5. Therefore, it appears plainly obvious, Dhp 1 & 2 are about 'kamma' & 'results' and not about consciousness being the creator of the universe of sense experience.

6. As for the word 'dhammā', in India, it is a word that describes any religious path or mode of behaviour that people believe (either wisely or ignorantly) helps their life. In my opinion, 'dhammā' here means 'modes of behaviour'.

7. Therefore, I personally would translate Dhp 1 & 2 as follows:

1. Mind precedes all modes of behaviour. Mind is their chief; they are all mind-wrought. If with an impure mind a person speaks or acts suffering follows him like the wheel that follows the foot of the ox.

2. Mind precedes all modes of behaviour. Mind is their chief; they are all mind-wrought. If with a pure mind a person speaks or acts happiness follows him like his never-departing shadow.

As to the word manas, Thrangu Rinpoche said (paraphrasing):

All mental events—all thoughts, memories and anticipation of the future with all its emotions of happiness, sadness, excitement, and frustration takes place in the manas. It is the manas which differentiates and thinks and makes judgements about the perception. After the eye, ear, nose, tongue and tactile consciousness perceives an object, the manas judges the sensory perception with thoughts.

So the word manas here is used to drive home the idea that it is our mind -- in the sense of our outlook, our way of seeing and interpretation -- is what creates our reality.

In Tibetan Buddhism they have this notion called "pure perception" or "sacred outlook". It's a practice of seeing everything as expression of Buddha-Nature, without a taint.

When we see the world with pure perception, there are no enemies of ours, no aggression is provoked in us, no anger, no antipathy. The reality of our perception is pure. Then our reactions are pure, our karma is pure, and it results in peace.

But when our perception is tainted, we see a different reality, we are in a different world. So naturally this world provokes very different reactions in us, which lead to trouble.

It is our outlook that defines our reality, our actions, and its results.

This outlook is a state of mind.

This is what is meant here by the word manas.

If one speaks or acts out of an addled manas, dukkha follows him like the cart's wheel follows the ox's hoofprint.

...

If one speaks or acts out of a clear manas, sukha follows him like a shadow which never leaves.

Now, what exactly is addled/dirty manas and what is clear/pure manas?

Manas is not memory, it is only an organ of mental (inner, reflective) perception, thus supporting further interpretation and judgement - so how and why can it be dirty or clean?

Manas is exactly the part of mind where Upadana or Feeding occurs. Upadana is when we keep going over a certain idea or image or event, triggering our interpretation and emotional reaction again and again. As a result of this cyclic feeding, manas constantly keeps this idea "loaded", and presence of this idea affects or skews all new interpretation and judgment.

So the dirty manas or dirty outlook is what happens when we feed on negative, selfish, aggressive, divisive thoughts.

And the pure manas is when we don't feed, don't maintain these tainting dharmas (known as klesha or asava). As a result we see things yathabhuta - as they are. Seeing things as they are leads to right action, and right action leads to the ending of suffering and to harmony and peace.

This is why the subsequent verses of Dhammapada speak about (not) harboring offense and enmity, (not) dwelling on pleasant experiences, and eventually "vomiting all the asavas". These are examples of maintaining the dirty manas vs purifying it.