question #1 Sahih Muslim 378a, Book 4, Hadith 2 : What is the significance of repeating the phrases in the Adhan and Iqama in Islamic practice?

Bilal was commanded (by the Messenger of Allah) to repeat (the phrases of) Adhan twice and once in Iqama. The narrator said: I made a mention of it before Ayyub who said: Except for saying: Qamat-is-Salat [the time for prayer has come].