Sin

In the Abrahamic context sin is to defy the will of God.  The word for sin in Greek meant "to miss the mark."  And the view of most is that sins vary from minor sins to mortal sins which lead one to Hell.  However, Jesus said lust is as bad as adultery and that hate is equal to murder so Jesus doesn't seem to have this nuance human view point of sin.
And yet He calls us to follow Him and He forgave the sins of many He came into contact with.  He told group of men ready to stone an adulteress caught in the act that "He who is without sin may cast the first stone."  But Jesus is the only one who is sinless and yet He cast no stone and instead said He did not condemn her but told her to "go and sin no more."
Jesus is forgiving as long as each of us repent of our sins.  His forgiveness is perfect and infinite.
Jesus tells a story about sinners involving a tax collector(publican) and a Pharisee:
¹⁰ Two men went up into the temple to pray; the one a Pharisee, and the other a publican.
¹¹ The Pharisee stood and prayed thus with himself, God, I thank thee, that I am not as other men are, extortioners, unjust, adulterers, or even as this publican.
¹² I fast twice in the week, I give tithes of all that I possess.
¹³ And the publican, standing afar off, would not lift up so much as his eyes unto heaven, but smote upon his breast, saying, God be merciful to me a sinner.
¹⁴ I tell you, this man went down to his house justified rather than the other: for every one that exalteth himself shall be abased; and he that humbleth himself shall be exalted. luke 18:10-14
This forgiveness of Christ is possible not only because of His countenance but because of the eternal nature of the Atonement.  The Atonement is ongoing and eternal it is not some fixed point in time where it becomes used up and forgiveness runs out.
The Atonement is forever ongoing and all that is required is repentance and a humble attitude.  It is not as some would have it be, that every sin is dirt and grime that covers us and we can never be clean after certain sins.  The power of the Atonement washes us clean no matter how many times we miss the mark.
Jesus likens this to sheep who have been lost in Luke 15:1-10:
Then drew near unto him all the publicans and sinners for to hear him.² And the Pharisees and scribes murmured, saying, This man receiveth sinners, and eateth with them.
³ And he spake this parable unto them, saying,
⁴ What man of you, having an hundred sheep, if he lose one of them, doth not leave the ninety and nine in the wilderness, and go after that which is lost, until he find it?
⁵ And when he hath found it, he layeth it on his shoulders, rejoicing.
⁶ And when he cometh home, he calleth together his friends and neighbours, saying unto them, Rejoice with me; for I have found my sheep which was lost.
⁷ I say unto you, that likewise joy shall be in heaven over one sinner that repenteth, more than over ninety and nine just persons, which need no repentance.
⁸ Either what woman having ten pieces of silver, if she lose one piece, doth not light a candle, and sweep the house, and seek diligently till she find it?
⁹ And when she hath found it, she calleth her friends and her neighbours together, saying, Rejoice with me; for I have found the piece which I had lost.
¹⁰ Likewise, I say unto you, there is joy in the presence of the angels of God over one sinner that repenteth.
Notice that Jesus accepts repentant sinner while the Pharisees stand in permanent judgment of anyone who has sinned in a way they consider evil and forgive sins they think don't matter. 
Modern Pharisees perpetuate this idea of certain sins not mattering at all but there are deal breaker sins according to them.  Then there is the far worse idea of the "Not even once club."
The idea of striving to be perfect even though none of us are, this puts an unrealistic and unlivable burden on us that no one can live up to.  This is part of an honor/shame culture where outward signs of piety are honored and outward sinners are shamed, not loved or forgiven.
This is not what Jesus had in mind and yet His self proclaimed disciples are often the worst of offenders in terms of judgment, grudges and condemnation.  As opposed to what Jesus professed which was acceptance, forgiveness and love.
We are never so lost that we cannot be found, we are never so dirty that we cannot be washed clean.  We are never so sinful that we can't be loved.
We are all worthy of acceptance, forgiveness and love because we are all God's children.
Those who want to determine who is and is not worthy are professing the philosophies of men mingled with scripture.
It is not that being Christ-like is unreal, it's that our idea of what perfection means for us is what's imperfect.  Before you listen to people pointing their fingers make sure their hands are clean.
Ye have heard that it was said of them of old time, Thou shalt not kill; and whosoever shall kill shall be in danger of the judgment:
²² But I say unto you, That whosoever is angry with his brother without a cause shall be in danger of the judgment: and whosoever shall say to his brother, Raca, shall be in danger of the council: but whosoever shall say, Thou fool, shall be in danger of hell fire.
²³ Therefore if thou bring thy gift to the altar, and there rememberest that thy brother hath ought against thee;
²⁴ Leave there thy gift before the altar, and go thy way; first be reconciled to thy brother, and then come and offer thy gift.  Matthew 5:21-24
And here Jesus tells us that it is our job to forgive, and even that if we hold a grudge our offerings to God will be ignored.
So in response to being shamed, righteous indignation is not the path one should take, even if some sin by judging they need forgiveness because darkness cannot drive out darkness only light can do that and hate cannot drive out hate, only love can do that.
By reacting in this way it shows rather than tells others what is really important and it leads people by example.  Which is the way Jesus taught us best.