Why did God choose Abraham for His covenant instead of other righteous men of his time, such as Melchizedek?

In Genesis, Abraham is chosen by God to be the father of many nations and the one through whom the covenant is established (Genesis 12:1–3; 17:1–8). However, at the same time, Genesis also introduces Melchizedek, king of Salem and "priest of God Most High" (Genesis 14:18–20), who is presented as a righteous and significant figure. Given that Melchizedek was already a priest of the true God, what does Scripture or Christian theology say about why God specifically chose Abraham—rather than Melchizedek or any other righteous men of that time—to make His covenant with? I'm looking for answers based on biblical evidence or theological reasoning, rather than speculation.