Avraham our Father was the founder of Judaism and monotheism. Why is Avraham considered the father when he is not the first one to believe in the Creator? We know that Noach (who built the ark on the Creator's direction) was monotheistic and his son Shem established a Yeshiva where Torah was taught. Avraham made a living from cattle and sheep. How does he come to be the father of monotheism and of Judaism?
Avraham is the father of monotheism because he spread monotheism to others. Avraham's predominant character trait was chesed (kindness)., both to the Creator and to people.
Avraham loved the Creator. The way he demonstrated his love for the Creator is by going around the world and telling people about the Creator. He and Sarah Imeinu were successful in showing people that there is one Creator, which led to them giving up their idols and to their becoming monotheistic.
How did he do this?
Avraham would invite people into his home, give them a nice meal. By extending kindness to people, he had an opportunity. At the conclusion of the meal, when the guests and travelers thanked him for his hospitality, he said "Please thank the One who really provided it, the Creator," and he elaborated. He proceeded to share more with them, and some were interested and some were not. The ones who were interested became monotheistic and maintained a connection to Avraham and to his teachings, and the others left, perhaps paying for the meal as a way to show their gratitude.