Concerning the first: there are two aspects to the relationship of this verse and the preceding ones:

The First: According to Ibn 'Abbas' commentary, when in order to prove divine unity [the Qur'an] says: "O you people! (Yâ ayyuhâ an-nâs)," it also proves the prophethood of Muhammad (Upon whom be blessings and peace), who was the clearest proof of divine unity. Now, prophethood is proven by miracles. And the greatest of miracles is the Qur'an. And the most subtle facet of the Qur'an's miraculousness lies in the eloquence of its word-order (nazm).

Muslims agree that the Qur'an is miraculous and inimitable. The authoritative scholars however differ as to the ways in which this is so. Nevertheless, these ways do not conflict, for some prefer one aspect [and others another aspect]. Some say that its miraculousness lies its predicting the future; according to others, it is its bringing together [all] truths and sciences; others assert it is its freedom from contradictions and defects; according to others, it is the originality of its styles and the singularity of the beginnings and ends of its verses and suras; others say it was its appearance from someone illiterate who could neither read nor write; according to others it was its being so extraordinarily eloquent as to be beyond human power; and so on and so forth. Detailed knowledge of this [latter] sort of miraculousness may be obtained by studying Qur'anic commentaries such as the present work, or it may be learnt summarily in [the following] three ways, as it was ascertained by 'Abd al-Qâhir al-Jurjânî, the Master of Eloquence (al-Shaikh al-Balâgha), and al-Zamakhsharî, and al-Sakkâkî, and al-Jâhiz:

The First Way: The Arab people were illiterate nomads [who lived] in an unusual environment that suited them. They were awaked by the mighty revolutions [occurring] in the world. Their [only] books (dîwânuhum) [of their proud exploits consisted of] poetry and their [only] science was rhetoric (al-balâgha), and [the source] of their pride and vainglory was eloquent speech (al-fasâha) in such fairs as 'Ukâz. They were the cleverest of peoples and therefore the most needy for mental exercise and activity, and mentally they were experiencing a period of burgeoning youth. Then the Holy Qur'an rose upon them with its majesterial eloquence and outshone their eloquence, represented by the Seven Hanging Odes (al-mu'allaqât al-sab'a), inscribed in gold [hanging] on the walls of the Ka'ba. Despite their being eloquent orators - the commanders of rhetoric and eloquence and rulers of correct Arabic - they could not dispute the Qur'an nor utter a single word in argument, despite the severe taunts of the Messenger (UWBP) and his rebuking and chiding them, and discrediting their intelligence, and provoking them over a long period, and his humiliating them although some of their orators' heads touched the skies in their pride and others reached the stars. So if they had not wanted to dispute [the Qur'an] and put it to the test and if they had not been aware of their impotence, they surely would not have remained silent. Their total inability [to dispute the Qur'an] was therefore proof of its miraculousness and inimitability.