Eschatology: Church and Israel (Genesis 15; Galatians 3: 18-29)

The Lord calls Abraham out of his father’s house while giving a significant promise to Abraham: he would be the father of a multitude. Does the Lord's promise to Abraham apply only to the direct genealogical descendants of Abraham? Is the promise bigger than Abraham's genealogy? Is the church a different promise or is the church living out of the same promise made to Abraham? Who are Abraham’s children?