We have Abraham as our father: Some Jews believed that being part of Abraham's family line guaranteed their salvation (see John 8:33–39; Acts 7:2; Romans 4:1).
And do not begin to say to yourselves, 'We have Abraham as our father.': God chose the Israelites as his people, but he could reject them. If he wanted, he could create children of Abraham from these very stones (compare Hosea 1:3–9; Romans 9:6–8, 27–28; 11:17–21).