4 For in the case of those who have once been enlightened and have tasted of the heavenly gift and have been made partakers of the Holy Spirit, 5 and have tasted the good word of God and the powers of the age to come, 6 and then have fallen away, it is impossible to renew them again to repentance, since they again crucify to themselves the Son of God and put Him to open shame. 7 For ground that drinks the rain which often falls on it and brings forth vegetation useful to those for whose sake it is also tilled, receives a blessing from God; 8 but if it yields thorns and thistles, it is worthless and close to being cursed, and it ends up being burned.
-—Hebrews 6
But does this mean that they were saved, or merely attending religious services and making an outward appearance, but their hearts were not changed?
The Pharisees thought they were believers, and followed the customs and rituals of the Jews, but when they came in contact with Jesus Christ, they were exposed for unbelievers that they were.