What does Matthew 8:12 mean?

This completes a sentence begun in the previous verse (Matthew 8:11). Responding to the Roman officer's faith in Him, Jesus has said that many Gentiles will share a table in the kingdom of heaven with Israel's patriarchs. Now He adds that the "sons of the kingdom" will not be there, cast into outer darkness where there will be weeping and gnashing of teeth.

The phrase "sons of the kingdom" was a Jewish term for the nation of Israel. Jesus is teaching that simply being born into the nation of Israel will not guarantee someone a place in heaven, as was commonly thought among the Jewish people (Galatians 3:7–9). Instead, Jesus is emphasizing that faith in Him—faith like that of the Roman centurion—will be the deciding factor about who is allowed into the kingdom (Galatians 3:28–29).

Jesus is not saying all Jewish people will be excluded from heaven. After all, the patriarchs will be there. Many Jewish people will come to put their faith in Jesus. His point is simply that citizenship in Israel will not provide anyone a place at the table.

Jesus goes even further. Those not allowed into the kingdom of heaven will be thrown out into a place of darkness and misery. "Weeping and gnashing of teeth" is language Jesus uses regularly to describe the suffering in hell (Matthew 13:42; 22:13; 24:51; 25:30).