Paul"s second question was this. God will not forsake His promises to bless the nation since some of the Israelites proved unfaithful, will He? The objection Paul voiced calls attention to the promises God had given Israel in the Old Testament covenants. These too constituted an advantage for the Jews. [source][source][source]
By referring to the unbelief of the Jews ( Romans 3:3) Paul was looking at the root of their unfaithfulness to God. Of the generation that received the law at Sinai, for example, only two adults proved faithful, Caleb and Joshua. Still God brought the whole nation into Canaan as He had promised, though the unbelieving generation died in the wilderness. [source][source][source]
Paul agreed. God would remain "true" (true to His word, reliable, trustworthy) to bless Israel as He had promised ( Romans 3:4). God would even be faithful if everyone else proved unfaithful, not just if some proved unfaithful. Paul cited David"s testimony to God"s faithfulness after David"s own unfaithfulness as historic, biblical support. [source][source][source]