Genesis 12-17: A Blessing

Now the LORD had said to Abram:
“Get out of your country,
From your family
And from your father’s house,
To a land that I will show you.
I will make you a great nation;
I will bless you
And make your name great;
And you shall be a blessing.
 I will bless those who bless you,
And I will curse him who curses you;
And in you all the families of the earth shall be blessed.”  - Gen 12:1-3 NKJV
Part of this blessing was very evident to Abram shortly after the Lord spoke to him.  He began to wander.  He went from place to place and back again, building altars along the way.  Abram could see in his wanderings that blessing and curses went with him.  He saw Pharaoh's house become diseased when Pharaoh took Sarai for his wife.  He rescued Lot and a host of others when they were captured by the four kings who took Sodom and Gomorrah.  Sometimes when he stopped wandering long enough to build an altar, the Lord would speak to him again as in Genesis 15 when God tells Abram "Do not be afraid, Abram. I am your shield, your exceedingly great reward.”.  But by this time, Abram no longer believed the Lords promise that he would become a great nation.  It seemed that the only possibility of descendants lay with Hagar, his wife's servant.   
That was not what the Lord God had in mind  He said he would make his name great,  but in order for Abram and Sarai to have offspring, their names would have to be changed.  Their new names, Abraham and Sarah, retained the roots of their former names, but Abram which means 'father' became 'father of many' and Sarai which means 'princess' became 'princess of multitudes'.  A name change and the whole of their story would be different.