I've written to previous articles on this at these two posts:
On these previous lessons, I discuss some of the ancient stories found outside the scriptures regarding Abraham.
Abraham's Search for the Priesthood
The Book of Abraham gives a very detailed and concise introduction.
You can read in the above links some of the reasons why Abraham was forced to find another residence. His battles with Nimrod over who held the true power of God are a key to this. Whenever a people become very wicked, the righteous are often removed by God and sent to a Promised Land. The whole people, including his fathers had turned from righteousness and towards idol worship. In Abraham's time, Ur of Chaldea was a large city set on the banks of the Euphrates river and on the Persian Gulf as a mighty port (it is now inland). It was a major economic center centuries before Abraham. The Deity of Ur was Sin or Nanna, the Moon. However, there were many gods worshiped within the walls of the city by the various peoples in the area.In the land of the Chaldeans, at the residence of my fathers, I, Abraham, saw that it was needful for me to obtain another place of residence;And, finding there was greater happiness and peace and rest for me, I sought for the blessings of the fathers, and the right whereunto I should be ordained to administer the same; having been myself a follower of righteousness, desiring also to be one who possessed great knowledge, and to be a greater follower of righteousness, and to possess a greater knowledge, and to be a father of many nations, a prince of peace, and desiring to receive instructions, and to keep the commandments of God, I became a rightful heir, a High Priest, holding the right belonging to the fathers.It was conferred upon me from the fathers; it came down from the fathers, from the beginning of time, yea, even from the beginning, or before the foundation of the earth, down to the present time, even the right of the firstborn, or the first man, who is Adam, or first father, through the fathers unto me.I sought for mine appointment unto the Priesthood according to the appointment of God unto the fathers concerning the seed.My fathers, having turned from their righteousness, and from the holy commandments which the Lord their God had given unto them, unto the worshiping of the gods of the heathen, utterly refused to hearken to my voice (Abr 1:1-5)
For many, the variety of gods provided a comfortable living. Abraham's father was one of those known to make idols to sell to the people. For many, personal wealth guided worship, it seems.
However, Abraham discovered that true happiness came through seeking out the real God. He sought for the "blessings of the [righteous] fathers" (Noah, Melchizedek, etc).
Through faithful and righteous living, he gained many of his desires in his life, however many were left to be fulfilled after his death.
The revelations he received, such as his understanding of Creation and Cosmos that we find in Abraham 3-4, allowed him to teach the Egyptians, who developed intricate math algorithms to build their cities, pyramids, and other magnificent structures. It seems that being a "father of many nations" is tied to having a greater knowledge of the things of God. Interestingly, even though Ur was founded 1-2 thousand years before Abraham, he sought what he believed was an even more impressive timeline of priesthood power going back to the first father, Adam.
Right of the Firstborn
With this came the "right of the Firstborn" (Adam). Abraham saw Adam and Eve as the first children born of God into mortality. In reaching back to the beginning of time, he stretched forth into the Meridian of Time to the second Adam, where Jesus Christ became the Firstborn of the Father in the flesh, and to the end times when Christ will bring together the Church of the Firstborn: all those who (as with Abraham), have sought the blessings and power of the priesthood and fulness of the gospel, have received through revelation an increased knowledge of the things of God, and through faith and righteousness have gained the power to do all things necessary to return back to God's presence.
For us today, as we seek the rights of the Firstborn, and do so in the correct manner (as many seek to obtain God's power for unrighteous purposes), we become as Abraham and Adam: among those counted as the First born of God. The firstborn received a bigger portion of the inheritance than did others who were not given this blessing. For Abraham, this included being the father of many nations, to have innumerable descendants. To rule over more than just a few water holes in the desert, but to rule with God over all things.
As we seek the God of Abraham, and the God of Isaac, and the God of Jacob, we will also be blessed with being one of the first born, receiving all blessings promised to them and more.