Find the most dedicated Jew or Muslim and you probably won’t find anyone more dedicated to God under his moral Laws than the Apostle Paul before he became a Christian. Paul said he was blamelessly devoted to God before knowing Christ but after becoming a Christian he counted all that devotion as mere rubbish:
If someone else thinks they have reasons to put confidence in the flesh, I have more: circumcised on the eighth day, of the people of Israel, of the tribe of Benjamin, a Hebrew of Hebrews; in regard to the law, a Pharisee; as for zeal, persecuting the church; as for righteousness based on the law, faultless. But whatever were gains to me I now consider loss for the sake of Christ.
But whatever were gains to me I now consider loss for the sake of Christ. What is more, I consider everything a loss because of the surpassing worth of knowing Christ Jesus my Lord, for whose sake I have lost all things. I consider them garbage, that I may gain Christ (NIV Philippians 3:4-9 Bold mine)
Pharisees in the Bible were precisely known for the ‘incredible and exceptional level of devotion to God’, a level of devotion which most could not personally dare to imagine or undergo.
We sometime forget how dedicated they were and how much respect they obtained from the general population for that 'holy behaviour'. We forget this wisely, because Jesus said doing holy things for God for the respect that man will provide is evil. This respect you have is what a self-righteous person works for, so they would be very happy to hear you speak this way. However, Jesus looked at it quit differently. If good works are not done by faith in Messiah, they are not done by faith in God. Also anything that is not done by faith is sin, therefore all good deeds done in unbelief is not good at all -- it is sin -- and the deadliest kind -- for it makes a person self-righteous.
everything that does not come from faith is sin. (NIV Romans 14:23)
And without faith it is impossible to please God (NIV Hebrews 11:6)
Jesus took a different view to those 'committed to God', but were not committed to faith in Him, for the forgiveness of their terrible and huge sins.
Religious people without faith in Christ can be very dedicated in converting others to their zeal for God:
“Woe to you, teachers of the law and Pharisees, you hypocrites! You travel over land and sea to win a single convert, and when you have succeeded, you make them twice as much a child of hell as you are. (NIV Mathew 23:15)
Religious people without faith in Christ can sacrifice many material things in their devotion to God:
“Woe to you, teachers of the law and Pharisees, you hypocrites! You give a tenth of your spices—mint, dill and cumin. (NIV Mathew 23:23)
Religious people without faith in Christ can sacrifice impress others by outwards commitments to God, but their unrepentant hearts by rejecting Christ shows the true state of their inwards perversity:
“Woe to you, teachers of the law and Pharisees, you hypocrites! You clean the outside of the cup and dish, but inside they are full of greed and self-indulgence. (NIV Mathew 23:25)
Religious people without faith in Christ seem like very good people and its sometime hard to tell what is going on inside but Christ shocked everyone by having a fiery discernment:
“Woe to you, teachers of the law and Pharisees, you hypocrites! You are like whitewashed tombs, which look beautiful on the outside but on the inside are full of the bones of the dead and everything unclean. (NIV Mathew 23:27)
I could keep going and going but I think you get the point.
Some of these highly impressive people who were extremely dedicated to God at the times of the Apostles had doubts whether Jesus was the Messiah, or not. Some had converted to Christianity but not with real sincere faith yet. Their religious convictions and how they perceived the faith of their holy forefathers made them seriously doubt the gospel. There were struggling with a deadly poison - unbelief. It was a heaven, or hell, tuype of decicision.
The Epistle to the Hebrews (Jewish people) was written to them, to ensure they do not get confused. In that Epistle we find some of the most severe warnings in all of scripture, because turning away from Christ to Judaism is exposing your soul to the danger of hell – with a sort of 'fast track' direction. For having been exposed to the truth anf grace of Christ and then rejecting it! and turning to another religion is possibly the greatest sin a man can commit.
If we deliberately keep on sinning after we have received the knowledge of the truth (i.e. turn away from faith in Christ and return to Judaism), no sacrifice for sins is left, but only a fearful expectation of judgment and of raging fire that will consume the enemies of God. Anyone who rejected the law of Moses died without mercy on the testimony of two or three witnesses. How much more severely do you think someone deserves to be punished who has trampled the Son of God underfoot, who has treated as an unholy thing the blood of the covenant that sanctified them (i.e. disrespecting the blood that brought them into an external knowledge of the gospel, offering them eternal life which they were about to possibly reject!!), and who has insulted the Spirit of grace? For we know him who said, “It is mine to avenge; I will repay,” and again, “The Lord will judge his people. ”It is a dreadful thing to fall into the hands of the living God. (NIV Hebrews 10:26-31 Italics mine)
So you see there is nothing here but a disappointing answer. The Bible does not just sprinkle sugar on all our fears and worries. Sometimes it says something pretty tough, and I know this can be very hard at times. The Bible has knocked me down many times, but God’s love pulls me back up! The Bible wants us to 'hang in there' and 'do not get discouraged' about all this. Gods grace is much bigger than our sins, whether they are ‘white’ sins of self-righteousness like those in religion, or those lesser evils, those ‘black’ sins of sexual perversity, drunkenness, greed for money, etc.