If they continue not in their unbelief (ean mē epimenōsi tēi apistiāi). Third class condition with the same verb used in Rom 11:22 of the Gentile. Locative case of apistiāi here (same form as the instrumental in Rom 11:20).
For God is able (dunatos gar estin ho theos). See this use of dunatos estin in Rom 4:21 rather than dunatai. This is the crux of the whole matter. God is able.