As for "concentration is present in every citta" and thus it follows a suggestion about why develop it?"
I do hope that strong concentration is not required and that path is easier as opposed to harder. I am all for that...
However:
Do hell beings have "concentration"?
Do snipers have lots of concentration? If so, why aren't they awakened?
Why did the Buddha talk about DEVELOPMENT of concentration if it is alrady present?
If one teaches a Dhamma to a person down the street, will he achieve awakening?
There is a sutta that talks about achievement of stream while listening. If one notes carefully the requisites, then one will see that being free at that time from a defilement obstruction is a required thing. From what I remember, the dhutanga practices for example serve the purpose to suppress certain a defilements. Same for deep concentration on the level of 'access' and or above. Sure, concentration in and of itself doesn't make one awakened. But it can supress the a defilement obstruction AND creates lots of good kamma, so that when that person listens to the sutta, s/he could get awakened. Sure, some people may have been very pure by nature and didn't need to forcefully supress kilesas. Not everyone is like that...
"Endowed with these six qualities, a person is incapable of alighting on the lawfulness, the rightness of skillful mental qualities even when listening to the true Dhamma. Which six?
"He is endowed with a [present] kamma obstruction, a defilement obstruction, a result-of-[past]-kamma obstruction; he lacks conviction, has no desire [to listen], and has dull discernment.
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