Abraham received abundant blessings because he obeyed God. First, God gave Abraham's descendants the ability to conquer their enemies. Second, God promised Abraham children & grandchildren who in turn the whole earth would be blessed. People's lives would be changed as a result of knowing Abraham & his descendants. Most often we think of blessings as gifts to be enjoyed. But when God blesses us, his blessings are intended to overflow to others.
Reference summary used from the KJV Life Application Bible, Tyndale House Publishers, Inc., Wheaton, Illinois