What makes a circumstantial reading of jāʾa Zaydun wa-l-maṭaru yanzilu plausible?

Appendix to Faṣl and Waṣl: Circumstantial Clauses, Wāw and Pronominal Linkage

• Rain is another name for Zayd
• Rain is the subject of jāʾa
• The phrase is only an oath
• Rainfall can be the attendant background of the arrival