Romans 10:19

‘But I say, “Did Israel not know?” First Moses says, “I will provoke you to jealousy with what is no nation, with a nation void of understanding will I anger you.'

The switch here to addressing Israel tends to confirm that what has been said previously was directed more widely, that is, as speaking to both believing Jews and Gentiles. So the question now is, but what about (unbelieving) Israel? Did they not know? That raises the issue of what it was they were supposed to know. In context there are two main possibilities. The first is as to whether they knew the message about the Messiah. That has been answered in Romans 10:2. They were ignorant of God's righteousness, brought by the Messiah. The second is as to whether they knew that God's word would go out to the Gentiles. That might be seen as answered in Romans 10:14. (It is also answered in Isaiah 2:2; Isaiah 49:6; Isaiah 60:3; etc). In view of the fact that it is the preaching of the Gospel about the Messiah to the Gentiles which will arouse Israel to jealousy (Romans 11:11; Romans 11:14), the first would appear to be more likely. For here Paul does cite Scripture authoritatively, when he declares what ‘Moses said' (see Deuteronomy 32:21). And what did Moses say? He said that God would provoke Israel to jealousy by means of a ‘no-nation', and would anger them by means of a nation ‘void of understanding', that is one that did not know the Law (something which the followers of Jesus were accused of (John 7:49) and was clearly applicable, as well, to Gentiles). But in order to be provoked to jealousy in this way Israel had to have become cognisant of what was being proclaimed. Thus it is clear that they did know what the messengers of the Messiah were teaching.