Someone once said that there are only two possible outcomes from believing in salvation by works. One is arrogance and the other is fear. Arrogance is the attitude of the spiritually proud who have deluded themselves into thinking that they’re good enough to earn God’s favor on their own merits. Fear is really the only logical conclusion for the rational person, because that person knows he can never be sure of measuring up. You seem to fall into the second category.
Preachers who would themselves stand condemned under their own interpretation of Scripture love to play on our fears. Salvation is not based on some sliding scale of virtue where as long as you don’t sin too often you’re still OK. The Bible is very clear in describing an impossibly high and exact standard of behavior. If anybody even think about sinning, you’ve sinned (Matt. 5) and as soon as you’re guilty of one sin, you’re guilty of all (James 2:10). Based on that, we’d all be irretrievably lost.
These people also love to judge others and find them wanting, another violation of Scripture, which tells us to leave that to the Lord (1 Cor. 4:5) and to focus on making sure that we’re OK before looking at anyone else. (Matt. 7:5) This kind of teaching encourages people to compare themselves to others rather than the standards of Scripture.
The Bible is equally clear that salvation is by grace alone, based solely on our belief that Jesus died in our place. Anything beyond that is a matter between the believer and the Holy Spirit working out the process of sanctification.
I suspect that there are many who are believers in name only and have not met the one standard that God requires, to believe in the One He has sent (John 6:29) Jesus was talking about them in the verses you cited, because God’s will is clearly spelled out in John 6:38-40.
“For I have come down from heaven not to do my will but to do the will of him who sent me. And this is the will of him who sent me, that I shall lose none of all that he has given me, but raise them up at the last day. For my Father’s will is that everyone who looks to the Son and believes in him shall have eternal life, and I will raise him up at the last day.”
But the only sure measure of this is the hidden motives of our hearts, which only the Lord can discern. Behavior is an unreliable measure at both extremes. The Pharisees were extremely well behaved, but voted to execute the Lord for blasphemy, and tax collectors were notoriously corrupt but those who cried out for forgiveness went home justified. (Luke 18:10-14)
We’re saved because of what we believe, not because of how we behave.