How important is this subject to Gentile Christians of the 21st Century? If the importance of a subject can be measured by the amount of space given to it by God in the Scriptures, then this must be one of the most important of all subjects.
The Bible is filled with a revelation of His purpose concerning the people of Israel, the land of Palestine, and the city of Jerusalem. This purpose is illustrated in history, type and prophecy.
However, God’s purpose in Israel goes further back than Israel and his twelve sons. It really starts with “the call of Abraham”. But a purpose must have an existence prior to its manifestation or revelation! And so the author goes right back to the beginning, and finds the first revelation of this purpose in Genesis 3.