question #1 Sahih Muslim 379, Book 4, Hadith 6 : What is the significance of the phrases used in the Islamic call to prayer (Adhan)?

Allah is the Greatest, Allah is the Greatest; I testify that there is no god but Allah, I testify that there is no god but Allah; I testify that Muhammad Is the Messenger of Allah, I testify that Muhammad is the Messenger of Allah, and it should be again repeated: I testify that there is no god but Allah, I testify that there is no god but Allah; I testify that Muhammad Is the Messenger of Allah, I testify that Muhammad is the Messenger of Allah. Come to the prayer (twice). Come to success (twice). Ishaq added: Allah is the Greatest, Allah is the Greatest; there Is no god but Allah.