Acts 13:40

Beware therefore, lest that come upon you, which is spoken of in the prophets;

The warning belongs to Paul's Sabbath sermon in the synagogue at Antioch in Pisidia, where he traced the history from deliverance from Egyptian bondage forward to present Jesus as the promised Messiah and Saviour of the seed of David. That setting places the caution directly after the proclamation of Jesus as the promised Messiah to the Jews gathered on the Sabbath.

It confronted a Jewish opposition moved by envy and jealousy when the multitude and the whole city gathered to hear the message. That opposition expressed itself in contradiction and blasphemy, and in bigoted prejudice that Gentiles could not share religious privileges on equal terms and that God's blessing belonged to Jews alone. When they heard that the Messiah was to be a light to the Gentiles as well as the glory of Israel, rage took hold with distorted minds unfit to weigh evidence. By such a course they were putting the Word of God from themselves and judging themselves unworthy of everlasting life.

Those who so rejected would be left to blindness of mind and hardness of heart. The apostles would then turn without hesitation to the Gentiles. The Gentiles rejoiced that Christ acknowledged them as children of God.