Were it not for the calling of Peter to Cornelius` house and the conversion of Saul, it is doubtful that the believing Jews would have spread the Gospel to the gentiles.
Paul makes a statement here which is not exactly correct. The Lord promised Abraham that through his seed all nations would be blessed.
That seed is Christ Jesus - not the Jewish people.
The Lord`s Grace was and is extended independently of the actions of any man or group of men or any race or any nation.