Not as though ... - Not as though the promise of God had entirely failed. Though I grieve thus Romans 9:2-3, though I am deeply apprehensive for the nation, yet I do not affirm that all the nation is to be destroyed. The promise of God will not entirely fail.
Not all Israel - Not all the descendants of Jacob have the true spirit of Israelites, or are Jews in the scriptural sense of the term; see the note at Romans 2:28-29.