Allah said _"Allah made it not but as a message of good news for you and as an assurance to your hearts"_. This Ayah means, "Allah sent down angels and told you about their descent to encourage you and to comfort and reassure your hearts. You should know that victory only comes from Allah and that if He willed, He would have defeated your enemy without you having to fight them." For instance, Allah said after commanding the believers to fight,

ذلِكَ وَلَوْ يَشَآء اللَّهُ لاَنْتَصَرَ مِنْهُمْ وَلَـكِن لّيَبْلُوَ بَعْضَكُمْ بِبَعْضٍ وَالَّذِينَ قُتِلُواْ فِى سَبِيلِ اللَّهِ فَلَن يُضِلَّ أَعْمَـلَهُمْ سَيَهْدِيهِمْ وَيُصْلِحُ بَالَهُمْ وَيُدْخِلُهُمُ الْجَنَّةَ عَرَّفَهَا لَهُمْ

(But if it had been Allah's will, He Himself could certainly have punished them (without you). But (He lets you fight) in order to test some of you with others. But those who are killed in the way of Allah, He will never let their deeds be lost. He will guide them and set right their state. And admit them to Paradise which He has made known to them) 47:4-6.

Commentary

In the previous verses, the battle of Badr was cited in relation to the battle of Uhud. Briefly stated there was the unseen support from Allah Almighty given to Muslims. In the present verses, some details of that support have been mentioned. Also stated is the wisdom behind the sending of angels.