If you state:
‘Sin will not keep you out of Heaven but losing your faith will’ most automatically believe you believe in a licence to sin. I am in good company if people believe that. Paul was accused of the same!
Note which comes first in the order of the new covenant. The law is placed in your heart and mind, only because this has happened will your sins and lawless deeds be remembered no more.
The first part of the new covenant cuts out a licence to sin. The law God desires you to follow is written in your mind and placed on your heart at the point of conversion. Meaning, in your mind you instinctively know how God wants you to live and in your heart you want to live that way(for the law is now in your heart) It is no longer an external law written on tablets of stone but an internal law, one written on tablets of human hearts. Huge difference. An external law does not mean you in your heart want to obey it, an internal law is very different. We all commit sin, for none is perfect, but there is a difference between sin we hate which we will commit due to our inability to perfectly obey the letter of the law(for sin is the transgression of the law) and sin we at time choose to wilfully commit which we know is wrong. When you commit wilfull sin, your conscience is seered, for you are going against how you in your mind know you should live, and in your heart desire to live. For you cannot go against what is in your heart without being severely troubled by your conscience. You will have no rest, and no peace until you come before your Father in Heaven and tell him you are sorry for your folly, only then do you get your peace back. That is the safeguard that cuts out a licence to sin under grace, for believers have no righteousness of obeying the law/which is not committing sin.
But what if you made a shallow commitment to God? What if, you kept and kept following after the flesh and not the Spirit? What then? For you have not been born again in your flesh, it opposes the Spirit. You start off being tormented, you become miserable, depressed, for you know in your heart you are following the wrong way. Your heart becomes hardened, your faith suffers, and in the end it dies. You can no longer have faith in Christ, and that is your only righteousness before God. Because continually following after the flesh, robs you of looking to Jesus and trusting him that he is your righteousness before God, not your ability to obey the law.
Therefore, to say sin will not keep you out of heaven, but losing your faith will, is, strange as it may seem accurate.
It cannot be another way, for if you can only remain saved/righteous before God if you do not commit sin, then you have righteousness of obeying the law. Paul’s core message was relentless, no believer has righteousness of obeying the law.