|Pirkei Avot Chapter 5: Ramchal: Roots of Abraham|
There were 10 generations from Adam to Noah, to show the degree of His patience; for all those generations angered Him increasingly, until He brought upon them the waters of the Flood.
There were 10 generations from Noah to Abraham, to show the degree of His patience; for all those generations angered Him increasingly, until our forefather Abraham came and received the reward of them all. (Avot 5:2)
From the time of Adam until the Generation of Dispersion (Tower of Babel), the righteous never ceased teaching the truth to the public, such as, Chanoch, Metushelach, Shem and Aiver; warning them to rectify their ways.
Once their measure was so full, at the time of the Dispersion, God judged with Is attribute of Justice, that it was befitting that the Root Effort, to repair Adams sin, should end. No longer would everyone have the opportunity and power to repair the root of the world.
However Abraham alone was chosen because of his actions and elevated status to become a elevated and precious tree, with its own roots, roots connected to the original effort to repair creation.
Only those connected to Abraham's roots are able to access the Root of Repair. (Ramchal)