Thank you for the question on Abraham, “Abraham went from being a father without any children to being the father of many nations (Genesis 17:3-5). What does it mean?”
When God called Abram and Sarai to leave their city or region of Ur of Chaldea, God promised to him that he will became a father of a great nation (Genesis 12:2–3). This was fulfilled through Isaac who is one of the patriarchs for the nation of Israel.
The promise by God that Abraham will be the father of many nations is that through him he will be father other children who will become nations. Genesis unfolds this promise through his firstborn son, Ishmael who becomes the father of the Ishmaelites. Although he was rejected by God for Isaac to become the direct descendant of the Israelites. In Genesis 25, Abraham remarries after the death of Sarah. Through his wife, Keturah, other people groups are formed. “Abraham had taken another wife, whose name was Keturah. 2 She bore him Zimran, Jokshan, Medan, Midian, Ishbak and Shuah. 3 Jokshan was the father of Sheba and Dedan; the descendants of Dedan were the Ashurites, the Letushites and the Leummites. 4 The sons of Midian were Ephah, Epher, Hanok, Abida and Eldaah. All these were descendants of Keturah” (A searchable online Bible in over 150 versions and 50 languages). If one were to count his grandchildren that would include Edomites.
SUMMARY: The children of Abraham through Sarah, Hagar, and Keturah became people groups who later became a nation with territory.
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