Two Destructive Errors in Christian Thinking

I suppose it is because of the erroneous teaching of "grace" that there are two major misunderstandings of the Christian salvation. One is that a person once having "accepted Christ" can never be lost to God's purposes. The other is that everyone who is "saved" receives the same reward.
These two doctrines, that "once saved always saved," and the idea that there are no rewards in the Kingdom of God because we all are equal being "saved by grace," are as destructive concepts as could possibly be developed by God's enemies.
Obviously, if we cannot be lost to God's purposes once we "accept Christ, then a Christian who is tempted severely is likely to yield to Satan, being under the impression that no matter what he or she does the safety net is there.
Why this is not obvious to sincere preachers of the Gospel is beyond me.
As for the Scripture references, there are too many for me to list here. But I will present a few that ought to be enough to persuade any person who honestly is seeking the truth.
However, I am not sure of that, because the truth in this case is so threatening that people may just shut their eyes and minds. Also, in some cases, there may be ego involvement if one has a record of preaching "once saved always saved." In addition, I think there may be pastors who will not preach the truth because their members may leave to go to a more "loving" pastor.