Only in RCC teaching is there gradation of sin.
One of their religious teachers said ‘catholicism is like climbing a wall of glass’......
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If any one sees his brother committing what is not a mortal sin, he will ask, and God will give him life for those whose sin is not mortal. There is sin which is mortal; I do not say that one is to pray for that. All wrongdoing is sin, but there is sin which is not mortal. 1 John 5:16-17
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All sins are the same is only true insofar as they make you a law breaker in need of salvation which even the smallest sinner needs as much as the more profligate sinner.
Thus not all only are all sins the same in the sense of making you a culpable sinner, but all sinners are the same insofar as they are both sinners, who are helpless to earn salvation or escape eternal damnation. and thus must rest upon the risen Lord Jessus to save by His sinless shed blood, thanks be to God.
However, that there are differences in sins as regards the degree of evil, and of sinners, is very Biblical. This can be seen in the degrees of penalty, so that the punishment for a thief is not the same as for an idolator, adulterer or murderer. Abraham lying about Sarah being his sister (she was his half sister) versus wife, to save his skin, is not the same as Herod's slaughter of the the innocents, or the sin of Sodom, "because their sin is very grievous." (Gn. 18:20) .
And likewise there are worse sinners than others, based upon not only what manner of sin they engage in, but how this relates to the degree of light and ability given. Thus it is written that Manasseh king of Judah did wickedly above all that the Amorites did, (2 Kings 21:11) while it shall be more tolerable for Sodom and Gomorrha in the day of judgment, than for cities that saw such great grace as the Lord and His apostles manifested. (Mark 6:11)
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)
And likewise 'Woe unto you, scribes and Pharisees, hypocrites! for ye devour widows' houses, and for a pretence make long prayer: therefore ye shall receive the greater damnation." (Matthew 23:14)
And thus professed believers are overall held as the most accountable, and are thus given stern warnings against impenitent willful sin and drawing back in unbelief. (Gal. 5:1-4; Heb. 3:9,12; 10:25-39) And thus the lost will be "judged every man according to their works," (Revelation 20:13) in determining their sentence, while believers will rewarded or suffer loss of rewards based upon their labor in building the church. (1Cor. 3:8ff)