Many christians famously say “sin is sin,” as if there is no actual distinction. Yes, all sin is wrong, all sin is a violation of the Father’s will, but scripture is clear that all sin is not the same.
In fact, there are several different words in the original scriptures that all got translated in your English version as “sin.” Those words have different meanings. This is at the core of one of the many false doctrines of christianity—the conflation of justification and sanctification.
If “sin is sin,” and there is no difference in one sin versus another, then explain why some sins are “sins not leading unto death,” but there’s “a sin that does lead to death” (1 John 5:16-17). What’s the difference there? Obviously there has to be some sort of distinction.
When folks declare a “changed life” as evidence of salvation, they use that same error, as works are not the basis of salvation. Lost people can change their lives as well. Justification (salvation) has nothing to do with one’s works, but with one’s belief.
Before one has been justified (made righteous), it is nonsense to preach “right living” to him, as that has nothing to do with whether he will receive eternal life. So, all those fiery preachers who scream from their pulpits about lost people needing to stop committing sins of the flesh (drunkenness, adultery, lying, stealing, etc.) are just preaching a false salvation of works.
Sins NOT leading unto death are all sins of the flesh (those things the preacher in the previous paragraph was screaming about), and they affect a believer’s relationship and reward, but they have nothing to do with eternal destiny. One who is truly born again (indwelt by the Holy Spirit) has eternal life, and will never be sent to hell.
The ONLY SIN that sends anybody to hell is unbelief (Hebrews 3:19); and, according to 1 John 5:10, that is everyone who has not received the Holy Spirit. A believer, in the Father’s eyes, is one who has the “evidence” placed within him—he has received the witness (testimony).
So, all sin is not the same—most sins have nothing to do with going to heaven or hell, as there is only one sin that condemns eternally (John 3:18). The rest do not affect eternal destiny (Matthew 12:31).
For more information: Do Sinners Go to Heaven?