"Very simply scripture does teach that there are differences in sins, both in the OT (Old Testament) and in the NT (New Testament). In the OT, if you read carefully in the laws given to Moses, the only punishment for known sins commited on purpose is death. For sins committed in ignorance, when it becomes known, a way is provided to make atonement for them usually by means of a sacrifice.
In the NT, there is a sin, which is NOT unto death (I John 5:16), but there is also a sin, which is unto death.
All of us are or have been sinners, but not all of us are reprobates. God is no respecter of persons. He treats everyone the same. But... all of us are not the same. We are not the same because we started out with different make-ups and we walked down different pathways making different decisions.
If I as an old believer were to decide to and then go ahead and chew out another person for falling short of God's glory, the judgment of God upon me would very likely be harsher than it would for the person who did the same thing the first day of his walk with God.
Consider also how many times the natural children of Jacob [israel] provoked God before He cut them off from the promised land. In the case of Moses, he lost his entrance to the promised land for one transgression.
"But he that knew not, and did commit things worthy of stripes, shall be beaten with few stripes. For unto whomsoever much is given, of him shall be much required: and to whom men have committed much, of him they will ask the more." Luke 12:48