Abraham was the son of an idol maker in Ur. He questioned polytheism, and had a theory of monotheism. So he left his father, ruining his father's idols as he went, and taking with him a small number of friends and relations. They wandered through the desert, and eventually Abraham found out who the one God is.
He had a conversation with God, in which they created a covenant (a sacred promise, treaty, arrangement). Abraham promised God that he will spread word of one God. (God made Abraham show complete devotion: God forced Abraham to sacrifice his first son (Isaac), but then an angel stopped the sacrifice.) In return for Abraham's devotion, God will “multiply” Abraham and give descendants land. Eventually Abraham and company settled in Canaan.
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