Therefore no one will be declared righteous in his sight by observing the law; rather, through the law we become conscious of sin.
We must walk a fine line as Christians. We need to point out sin in others while recognizing that we too sin. We must point out sin to non-Christians because only when they recognize their sin will they become aware of their need for a savior.
Likewise, we point out sin to Christians because even though our salvation may be secure, sin still damages our relationship with the Lord. Furthermore, it has earthly consequences that can lead to anything from physical harm to damaged relationships to imprisonment or even death.
We have many good reasons for preaching about the hazards of sin and warning Christians and non-Christians alike about it. The danger lies in believing that we are better than others who still fall victim to the temptations of any particular sin that we have mastered.
To begin with, we all struggle with sin. Some just struggle more than others and some struggle with sins that we do not. We must not preach about as if we are better than those who commit the sins that we preach against.
Instead we must remember that we are all sinners in need of grace. By teaching others about their sin, we hope to correct bad behaviors and bring people to repentance. This should always be the goal of preaching about sin. We should never be like the Pharisees and pretend that we are better than others who commit a certain sin that we preach against.