The Qurayshi army arrive in Medina and are stumped by the trench, and persuade the Jewish tribe of Banu Quraydha in Medina and convince them to betray their oath of neutrality
The Muslims stand vigilant day and night to defend the trench, even missing their obligatory prayers.
Surah 33, Al Ahzaab captures the tension, covering the hypocrites who exposed themselves when they saw the pagan army, and the believers who saw the army as confirmation of what Prophet Muhammad had said to them.
Amr ibn al-Wadd, a feared warrior, crosses over the trench and calls for one on one combat. Imam Ali ibn Talib is the only one who's willing to answer and defeats him in combat.
Lessons: - Do not broadcast and sensationalize evil, even if it is true, unless there's a benefit in making it public - Trust Allah and know that there is something positive in every difficulty and hardship

Lecture notes available at http://www.why-quran.org/?p=582.

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