What is the interpretation of the Noble Verse: (O you who have believed, say not "Ra'ina" but say "Unthurna")?

Muslims used to say to the Prophet, peace and blessings be upon him: "Ra'ina" meaning: "Watch over us and protect us." However, in the language of the Jews, this was a derogatory term, and it was also said to mean "foolishness." So, they (the Jews) would secretly say it to the Prophet, peace and blessings be upon him, while laughing. When Sa'd ibn Mu'adh learned of this, he threatened to strike the neck of anyone who said it. Then, the verse was revealed, prohibiting Muslims from saying "Ra'ina" so that they would not resemble the Jews in using a word by which they intended a corrupt meaning.