Genesis 15:1-6 / God's promise

When Abram hears the words of the Lord, he questions.  He questions how it can be that he is to have an offspring, since it has been a period of time since God said those words to him first in Genesis 12:7.  Abram presumes one of the men from his house will inherit everything and God responds correctively, “your very own son shall be your heir.”  God has promised Abram will have a son, and therefore it will be his son, and this will be the child of the promise.