Tafsir of Al-Anbiya' 21:61

They said: "Then bring him before the eyes of the people that they may testify.'' meaning, in front of a large audience so that all the people could be present. This was Ibrahim's ultimate purpose, so that he could tell this great gathering about the extent of their ignorance and how foolish they were to worship idols which could not defend themselves from harm or help themselves, so how could they ask them for help!

قالوا أأنت فعلت هذا بالهتنا يا إبراهيم