Tafsir of Al-Jinn 72:16

{And that if they had remained on the way} etc., is definitely conjoined to His saying, Glorified is He: "That a group of the jinn listened." The precedence of the conjoined clause over the non-conjoined—according to the opinion that permits it—causes no harm, due to the clarity of the situation and the absence of confusion.

"That" (an) is the lightened form of the heavy (mushaddadah), and its pronoun is the pronoun of the state/matter (dameer al-sha'n). Al-A’mash and Ibn Wathab read the letter 'waw' in "law" with a damma. The meaning is: "And it was revealed to me that the matter is: if the humans and the jinn—or both of them—had remained..."

{On the way}, which is the religion of Islam.

{We would have given them abundant water to drink}, meaning: much water. Asim, in one of the narrations of Al-A’mash, read it with a kasra on the 'dal'. The intent is: We would have expanded their provision for them. The mention of abundant water is specified because it is the foundation of livelihood, and its abundance is the foundation of prosperity; for it has been said: "Wealth is where there is water," and due to its scarcity among the Arabs.