http://www.quranreading.com/blog/the-great-significance-virtues-and-rewards-of-adhan/
Benefits of Adhan
1. There is a great rank of Muezzin (the one who invites to Namaz) in the Religion of Peace. Abdullah bin `Abdur-Rahman reported: Abu Sa`id Al-Khudri (R.A) said to me:
“I see that you like living among your sheep in wilderness. So whenever you are with your sheep or in wilderness and you want to call Adhan, you should raise your voice because whoever hears the Adhan, whether a human or jinn or any other creature, will testify for you on the Day of Resurrection.” Abu Sa`id added: “I heard this from the Messenger ﷺ of Allah.” (Bukhari)
It means that the Caller of Salah will benefit from the greatest bounties of Allah SWT on the Day of Resurrection, as everyone who hears him saying Adhan will testify in his favor on that day.
2. Abu Hurairah (May Allah be pleased with him) reported: The Messenger of Allah (sallallaahu ’alayhi wa sallam) said:
“When Adhan for Salat is pronounced, the devil takes to his heels and breaks wind with noise so as not to hear the call. When the Adhan is finished, he returns. When the Iqamah is announced, he turns his back, and after it is finished, he returns again to distract the attention of one and makes him remember things which he does not recall in his mind before the Salat, and says `Remember this, and this,’ and thus causes one to forget how many Rak`at he performed.” (Bukhari and Muslim)
This Hadith shows that Adhan is not any simple announcement; rather it is that powerful in its effect that Shaitaan (Satan) cannot bear hearing it as it contains the message about righteousness and leads one towards spirituality of heart and soul.
3. Abdullah bin `Amr bin Al-`As (May Allah be pleased with them) reported:
“I heard the Messenger ﷺ of Allah saying, “When you hear the Adhan, repeat what the Mu’adhdhin says. Then ask Allah to exalt my mention because everyone who does so will receive in return ten rewards from Allah. Then beseech Allah to grant me Al-Wasilah, which is a high rank in Jannah, fitting for only one of Allah’s slaves; and I hope that I will be that man. If anyone asks Al-Wasilah for me, it becomes incumbent upon me to intercede for him.” (Muslim)
The above mentioned saying of the Holy Prophet ﷺ tells us about the huge advantage of duplicating the words said by Muezzin. It not only makes one able to get Allah`s blessings, but also leads towards achieving the Greatest Assistance one could ever get, i.e. the support of Rasulullah ﷺ in the hereafter.
So, to conclude, one can say that Islamic way of calling people towards prayers is not merely a method of collecting them at one place for venerating God, but also serves as a means of reminding Muslims about their utmost religious duty of carrying out Namaz. It also describes the entire Islamic faith, pays Homage to Allah SWT, and last but not the least portrays Salah as the best source of success.