Overall meaning :
Allah Almighty informs His Prophet, may Allah bless him and grant him peace, that He has sent down to him the Book with the truth and containing the truth to judge among people in accordance with what He teaches him in His Book, and forbids him to plead for the treacherous who betray their trust, directing him to implore His forgiveness, for He is the All-Forgiving, the All-Merciful.
He also forbids him to plead for those who wrong and deceive themselves by committing sins, stating that He does not like the treacherous and sinful who are much given to deceit and misdeeds.
Then, describing these treacherous people, He mentions that they hide from people when they commit their evil deeds, but they do not care to hide from Allah, though He is with them, fully aware of everything they do, especially when they plot in the dark of night, saying things which are not pleasing to Him and which He does not approve. Allah has knowledge of all their actions.
Allah then reproaches those among the believers who wrongfully plead for them, saying: You may well argue with people on their behalf and they benefit from that in this life, but who will plead and argue with Allah on their behalf when the evidence is established against them on the Day of Judgement? Who will then be their defender?