A remnant (a small group that remains) would be scattered among the nations. God would send them into many lands. There, they would bear witness to God’s faithfulness to his covenant (his promises to his people).
In those foreign lands, they would see the truth about their own hearts. They would understand how they had been unfaithful to God. They would hate their evil and detestable sins. Then they would know that God was serious when he warned that he would punish those who broke his covenant.
Some of those who came to know that the Lord alone is God might also see another side of his faithfulness. They might experience his readiness to forgive those who truly repent (turn away from sin).
In the book of Exodus, Israel came to know that the Lord is God through his mighty acts of rescue (see Exodus 6:7). He saved them from slavery in Egypt. But later, their actions showed that they had forgotten him. Now they would come to know him again, not only through rescue, but also through judgment.