Bible passage: Genesis 17:18-19
Written: As early as 1400 BC
In Genesis 17, God tells Abraham that Abraham's wife, Sarah, would give birth to a son and that Abraham should name the son Isaac. He also tells Abraham that Isaac will be the one who inherits the blessings - the everlasting covenant - that God bestows upon Abraham:
And Abraham said to God, "If only Ishmael might live under your blessing!" Then God said, "Yes, but your wife Sarah will bear you a son, and you will call him Isaac. I will establish my covenant with him as an everlasting covenant for his descendants after him." (Genesis 17:18-19, NIV)
This might not seem like a Messianic prophecy, but it is a prophecy, and it does involve the Messiah's lineage - his line of ancestors, although that connection is not explicitly stated in Genesis 17.
The prophecy informs Abraham that it will be his future son, Isaac, to be born of Abraham's wife, Sarah, who will inherit the covenant that God makes to Abraham in Genesis 17.
At the point in time in which Abraham receives this prophecy, he already has a son, Ishmael, through Sarah's handmaid, Hagar. And, at this time, Abraham was nearly 100 years old, and Sarah, who had never had any children, was 90-years old. So Abraham might be excused for thinking that Sarah would never have children, but God informs him that indeed she would.
We learn more about the details of God's covenant with Abraham in later chapters of Genesis, and in later books of the Old Testament, and we learn that they involve the birth of the Messiah, who would be a descendant of Abraham, through his son, Isaac.
The New Testament writers, Matthew and Luke, record genealogies of Jesus, through his adoptive father, Joseph, and through his mother, Mary. Both genealogies include Abraham and Isaac as descendants.
Genealogies were important during Biblical times. The genealogies that Matthew and Luke presented in the New Testament would have helped to convince people that Jesus was the Messiah who had been promised by the prophecies of the Old Testament, including the one in Gen. 17:18-19.