We must supply the omitted verb εδιωξα (pursued) from verse Romans 9:31. That explains the rest.

They stumbled at the stone of stumbling (προσεκοψαν τω λιθω του προσκομματος). The quotation is from Isaiah 8:14. Προσκοπτω means to cut (κοπτω) against (προς) as in Matthew 4:6; John 11:9. The Jews found Christ a σκανδαλον (1. Corinthians 1:23).