{Cast out} (ekbale). Second aorist active imperative of
ekball(935c). Quotation from  Ge 21:10  (Sarah to Abraham) and
confirmed in  21:12  by God's command to Abraham. Paul gives
allegorical warning thus to the persecuting Jews and Judaizers.
{Shall not inherit} (ou m(8820)kl(8872)onom(8873)ei). Strong negative (ou
m(885c) and future indicative). "The law and the gospel cannot
co-exist. The law must disappear before the gospel" (Lightfoot).
See  3:18,29  for the word "inherit."