Why did the Prophet Salih say in Surat Al-A'raf: "And I convey to you the message of my Lord" (وأبلغكم رسالة ربي) in the singular form, while Noah and Shu'ayb said: "I convey to you the messages of my Lord" (أبلغكم رسالات ربي) in the plural form?

The mention of "message" in the plural form for some messengers has three aspects: either it signifies the messenger's perseverance in conveying the message at different times, or because the message encompasses diverse meanings such as doctrines, admonitions, and rulings, or due to the messenger conveying what they were entrusted with along with the law of previous prophets. Al-Baydawi and Ibn Ashour have mentioned these aspects in their interpretations.