Abraham became known as “The Father of Many Nations” through a promise given to him by God.
In the Bible's book of Genesis, we are told of a man named Abram who was to be rewarded by God because of his faith in God. In Genesis 12:1-2, God told Abram to leave his country, his people and his family, and travel to a remote land.
Abram obeyed and traveled from the land of the Chaldeans, which is now called Iraq, to the land of Canaan, which would later become known as Israel. Because of his faith, God rewarded him with a promise that he would become known as the "father of many nations," meaning that he would be blessed with many descendants.
hope it helps..thx
Mahayana promotes the idea of not just enlighting ourselves but also other things as well that makes it appealing for the theravada.