In Genesis 17, the Lord changes Abram's name to Abraham and Sarai's name to Sarah. As one biblical scholar observes, "the name changes of the ancestors to Abraham and Sarah imply both the authority of the giver of the name and the new destiny or mission indicated by the new name." So, by changing Abram's name to Abraham, the Lord claims Abraham as his own. Likewise, the Lord gives Abraham a new mission, namely to be the "father of many nations," which is the very meaning of the name Abraham.
The covenant between God and Abraham is an extremely important part of our journey through the Bible, because it is through the descendants of Abraham that God's purposes are accomplished and ultimately the Messiah, the Christ, is born.