Genesis 22:2 says, “Then God said, ‘Take your son, your only son, Isaac, whom you love…’” Yet Genesis 16 records how Abraham became the father of Ishmael. In fact, it is in Genesis 21 (the chapter before the words “your only son”) that we read about how Ishmael was sent away from Abraham’s household. Some think that this is a contradiction. How can Abraham have two sons by the time that the events in Genesis 22 occur, yet the text specifically says that Isaac was Abraham’s only son?
This so-called contradiction is easily solved when we pay attention to the context of the book of Genesis. First off, the Hebrew word for “only” here is yachiyd, which has the meaning of “unique” or “only begotten” (special). Isaac is the unique, special son of Abraham. This fits perfectly with one of the major themes in Abraham’s story – the promise that God gave Abraham.
In Genesis 12:2-3, God promises Abraham that he would be blessed with descendants who would become a great nation. This nation (Israel) would go on to bless all peoples on the earth. This blessing to all the earth was Jesus Christ. Jesus and the nation of Israel were descended from Isaac, not Ishmael. The Hebrew mentioned above clarifies Isaac as the child of that promise. God told Abraham that Sarah would have a child in her (and his) old age. This child was Isaac. Isaac is the only son of the promise.
I want to note, however, that this does not mean that God did not love Ishmael. Genesis 21 tells us that God actually blessed Ishmael and cared for him.
Understanding the context of any Bible passage is important. When Genesis 22 refers to Isaac as Abraham’s only son it has the meaning of Isaac as the only son of the promise that would be fulfilled through their descendants. The promise and blessing recorded in Genesis 12 did not come through Ishmael.
 Bodie Hodge. “A ‘Sonny’ Day.” In Demolishing Supposed Bible Contradictions. Volume 2. Ken Ham, Bodie Hodge, and Tim Chaffey. (Green Forest: Master Books, 2011). Pg. 37.