"Indeed, those who oppose [yuhaduna]"—meaning: show enmity toward—"Allah and His Messenger, those will be among the most abased [al-adhallin]"—meaning: Allah will humiliate them.
"The matter descends"—meaning: the revelation—"between them"—meaning: "between the heaven and the earth"—"so that you may know"—by this revelation—"that Allah is over all things competent and that Allah has encompassed all things in knowledge"—nothing escapes His knowledge.
Muhammad said: "[In] knowledge" is in the accusative case as an emphatic verbal noun (masdar mu'akkid); the meaning is: He has known everything with [absolute] knowledge. This part concludes with the praise of Allah.
﴿إِن الَّذين يحادون﴾ يعادون ﴿اللَّهَ وَرَسُولَهُ أُولَئِكَ فِي الأذلين﴾ (ل ٣٥٦) يذلهم الله.