To be clear, all sin is the result of the weakness of the flesh. So, differeentiating between "living in sin" and "committing sins in weakness" is basically the same thing.
The Scriptures make a plain and clear distinction between those who commit a sin in weakness while living sanctified lives from those who continue living in any sin(s) to fulfill their lusts. The former is forgiven and saved, and the latter is condemned.
For instance:
1 John 3:7-9
7 Little children [
addressing and warning Christians],
let no one deceive you. Whoever
practices righteousness is righteous,
as he is righteous.
8 Whoever
continues in sin is
of the devil, for the devil has been sinning from the beginning. The reason the Son of God appeared was to destroy the works of the devil.
9 No one born of God
continues to live in sin, for God's seed abides in him; and
he cannot live in sin, because he has been
born of God.
Romans 1:32
Though they know God's righteous decree that those who
practice such things deserve to die, they not only do them but give approval to those who
practice them.
Romans 6:1-4
What shall we say then? Are we to
continue in sin that grace may abound? 2 By no means! How can we
who died to sin still live in it? 3 Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? 4 We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might
walk in newness of life.
Romans 6:12-14
12 Let not sin therefore
reign in your mortal body, to make you
obey its passions. 13 Do not present your members to sin as
instruments for unrighteousness, but present yourselves to God as those who have been
brought from death to life, and your members to God as
instruments for righteousness. 14 For sin will have
no dominion over you, since you are not under law but under grace.
2 Corinthians 12:21
I fear that when I come again my God may humble me before you, and I may have to mourn over many of those who sinned earlier and have not repented of the impurity, sexual immorality, and sensuality that they have
practiced.
Ephesians 4:19
They have become callous and have given themselves up to sensuality, greedy to
practice every kind of impurity.
But maybe you are trying to distinguish between the frequency of a person's sins? Would you say if a person sins in weakness once every day is living in sin? How about one sin per week? If frequency of sin is the measure, how often is too often?
1 John 3:7-9
7 Little children [
addressing and warning Christians],
let no one deceive you. Whoever
practices righteousness is righteous,
as he is righteous.
8 Whoever
continues in sin is
of the devil, for the devil has been sinning from the beginning. The reason the Son of God appeared was to destroy the works of the devil.
9 No one born of God
continues to live in sin, for God's seed abides in him; and
he cannot live in sin, because he has been
born of God.
But maybe you are trying to distinguish between one person's desire to not sin and another person's desire to sin. If so, how can it be argued that a person desires to never sin when it is obvious that their desire to never sin is overcome by their desire to sin in those moments of weakness?
If we
keep ourselves in God's Love, then God is
faithful and
able to keep the faithful from falling into temptation (
Jude 1:21-25);
in that, he will not allow us to be tempted beyond what we are able to bear (
1 Corinthians 10:13).
If a "Christian" lives in any sin, he shows that his faith is not genuine, that he does not love Lord Jesus, because he refuses to take the way out of temptation that God provides to every Christian.
Granted, a Christian may be deceived by his own flesh, or the words of others, to commit a sin; but a true Christian cannot live in any sin.
But maybe you are trying to distinguish between one person who fully commits to not sinning and another person who does not. At what point does a person's repeated failures to follow through on his commitment indicate that his commitment is worthless?
If a "Christian" deliberately continues in any sin, he is not saved; rather, he will be condemned.
1 John 3:9
No one born of God
continues to live in sin, for God's seed abides in him; and
he cannot live in sin, because he has been
born of God.
Hebrews 10:24-31 (WEB) 24 Let
us [
The “us” are believers, including the Epistle writer] consider how to provoke
one another [
Christians, including the Epistle writer] to love and good works, 25 not forsaking
our own [
Christians, including the Epistle writer] assembling together, as the custom of some is, but exhorting
one another, and so much the more as
you [
Christians] see the Day approaching. 26 For
if we [
Christians, including the Epistle writer]
sin willfully after
we [
Christians, including the Epistle writer] have received the knowledge of the truth, there remains
no more a
sacrifice for sins, 27 but a certain fearful expectation of
judgment, and a
fierceness of fire which will devour the adversaries. 28 A man who disregards Moses’ law dies without compassion on the word of two or three witnesses. 29
How much worse punishment do you think he will be judged worthy of
who has trodden underfoot the Son of God, and has counted the blood of the covenant
with which he was sanctified [
Christians who despise the blood of Christ by deliberate sin] an unholy thing, and has
insulted the Spirit of grace [
Christians insult the Spirit dwelling in them by their deliberate sins]? 30 For
we (
Christians, including the Epistle writer) know him who said, “Vengeance belongs to me. I will repay,” says the Lord. [
Deuteronomy 32:35] Again, “The Lord will judge
HIS people [
those who believe].” [
Deuteronomy 32:36; Psalm 135:14 31] It is a fearful thing to fall into the hands of the living God.
My point is this... there is no way for a human being to earn right standing with God through sin-avoidance or through commitment to sin-avoidance. Rightness with God is only through having our sins forgiven. The good thing is Jesus gives His perfect, holy, and righteous life to all that trust fully in Him so that they may serve Him in the newness of the Spirit without regard to the condemnation that otherwise would be theirs due to the sinfulness of their flesh.
The only "Christians" who are cleansed from all sins, sanctified by God, are those who walk in the light by
following Lord Jesus into a righteous life.
1 John 1:6-7 (WEB)
If we say that we have fellowship with him and
walk in the darkness,
we lie, and don’t tell the truth. 7 But
if we walk in the
light, as he is in the light, we have fellowship with one another, and the
blood of Jesus Christ, his Son,
cleanses us from all sin.
1 John 2:4 One who says, “
I know him,” and
doesn’t keep his commandments,
is a liar, and
the truth is not in him. 5 But
God’s love has most certainly been
perfected in whoever keeps his word. This is how
we know that we are
in him: 6 he who says he
remains in him
ought himself also to walk just like he walked.
1 Thessalonians 4:7-8
7 For God did not call
us [
Christians, including the Apostle Paul] to be
impure, but to
live a sanctified life. 8 Therefore, anyone who
rejects this instruction rejects God, not man. This is the very God
who gives to you his Holy Spirit.