The post contains answer to questions “What is talbiyah in Hajj? Why pilgrims recites Talbiyah during Hajj? What is the purpose of Talbiyah reciting at Hajj and Umrah?”
What is talbiyah in Hajj?
Talbiyah is a Muslims prayer that pilgrims began to recites loudly upon putting the Ihram. The purpose of Talbiyah reciting is to help pilgrims purify themselves of every worldly concern and strengthen their intention of performing Hajj only for the glory of Allah.
Both Sunni and Shia Talbiyah are same except that Shia’s Talbiyah ends in an extra Labbaik.
Source: Above answer is based on information given on Hajj Umrah Planner and Wikipedia.