"It is He who sent down," meaning: He established "tranquility," which is dignity, according to the exegesis of al-Hasan, "into the hearts of the believers so that they may increase in faith along with their faith," meaning: in belief along with their belief. This means: they believe in Him through all that has been sent down of the Quran.
"And to Allah belong the soldiers of the heavens and the earth," through whom He takes vengeance for some against others.