First Missionaries of the Gospel of the Kingdom of God

The first missionaries of the Gospel of the kingdom of God besides the Lord Jesus Christ's ministry were the 12 disciples sent out by Jesus two by two. They went told only to go to the lost house of Israel and not to the Gentiles or Samaritans, which would come later. Why? Also, Judas Iscariot was one of these preachers empowered by Jesus. How could that be? Also, the worse sin anyone could ever commit is to hear the gospel and not repent and believe. Sodom and Gomorrah will be beaten with fewer lashes in hell than these.