Allah said next,

[وَيُنَزِّلُ عَلَيْكُم مِّن السَّمَآءِ مَآءً]

(and He caused rain to descend on you from the sky.)

`Ali bin Abi Talhah reported that Ibn `Abbas said, "When the Prophet arrived at Badr, he made camp. At the time, there was a sandy piece of land between the idolators and the water (the wells at Badr). Muslims felt weak and the Shaytan cast frustration into their hearts. He whispered to them, `You claim that you are Allah's supporters and that His Messenger is among you! However, the idolators have taken over the water resource from you, while you pray needing purity.' Allah sent down heavy rain, allowing the Muslims to drink and use it for purity. Allah also removed Shaytan's whisper and made the sand firm when rain fell on it, and the Muslims walked on the sand along with their animals, until they reached the enemy. Allah supported His Prophet and the believers with a thousand angels on one side, five hundred under the command of Jibril and another five hundred under the command of Mika'il on another side.''

An even a better narration is that collected by Imam Muhammad bin Ishaq bin Yasar, author of Al-Maghazi, may Allah have mercy upon him. Ibn Ishaq narrated that, Yazid bin Ruwman narrated to him that, `Urwah bin Az-Zubayr said, "Allah sent rain down from the sky on a sandy valley. That rain made the area where the Messenger of Allah and his Companions camped firmer so that it did not hinder their movement. Meanwhile, the part that the Quraysh were camping on became difficult to move in.'' Mujahid said, "Allah sent down the rain on the believers before slumber overtook them, and the rain settled the dust, made the ground firmer, made them feel at ease and their feet firmer.'' Allah said next,

[لِّيُطَهِّرَكُمْ بِهِ]

(to clean you thereby) using it after answering the call of nature or needing to wash oneself, and this involves cleansing what is on the out side,

[وَيُذْهِبَ عَنكُمْ رِجْزَ الشَّيْطَـنِ]

(and to remove from you the Rijz of Shaytan,) such as his whispers and evil thoughts, this involves sinner purification, whereas Allah's statement about the residents of Paradise,

[عَـلِيَهُمْ ثِيَابُ سُندُسٍ خُضْرٌ وَإِسْتَبْرَقٌ وَحُلُّواْ أَسَاوِرَ مِن فِضَّةٍ]

(Their garments will be of fine green silk, and gold embroidery. They will be adorned with bracelets of silver) [76:21] involves outer appearance,

[وَسَقَـهُمْ رَبُّهُمْ شَرَاباً طَهُوراً]

(and their Lord will give them a pure drink.) [76:21] that purifies the anger, envy and hatred that they might have felt. This is the inner purity. Next, Allah said,

[وَلِيَرْبِطَ عَلَى قُلُوبِكُمْ]

(and to strengthen your hearts, ) with patience and to encourage you to fight the enemies, and this is inner courage,

[وَيُثَبِّتَ بِهِ الاٌّقْدَامَ]

(and make your feet firm thereby). this involves outer courage. Allah know best.