You are reading a tafsir for the group of verses 86:11 to 86:12
وَالسَّمَاءِ ذَاتِ الرَّجْعِ (I swear by the sky that rains...86:11) The word raj refers to 'the rain that comes down repeatedly'. In other words, the rain that comes down and stops and then returns.
He has revealed to you ˹O Prophet˺ the Book in truth, confirming what came before it, as He revealed the Torah and the Gospel