In the textual tradition of the Book of Genesis, God establishes an everlasting covenant specifically through Isaac and his future lineage, promising that he would be the father of nations and that royal kings would descend from him.
Biblical scholars and theologians note that because this explicit divine promise of a massive, multi-generational lineage was given before the command to sacrifice him, Abraham's willingness to obey demonstrated an absolute faith that God would miraculously preserve or resurrect Isaac to fulfill that covenant.