1 John 2:1

1 John 2:1 says, My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous:  John referred to those he was writing to here as little children, and I believe he may have been referring to those who were newborn Christians as well as who were actual children.  He said that they shouldn't sin, which should be the goal of all Christians, but that if they did, they had an Advocate in Jesus Christ the Righteous.  We will always fall short of not sinning, but when we do, if we have accepted Jesus Christ as our Savior and Lord, He will wash away our sins.  

Verse two adds, And he is the propitiation for our sins: and not for ours only, but also for the sins of the whole world.  John said that Jesus was the propitiation for our sins as Christians, but not only for ours but for the sins of the whole world.  Many people will go to hell having Jesus Christ die for their sins but never accepting His gift of salvation.  There is no one that Jesus Christ didn't die to bring redemption to, but everyone must accept His redemption for it to benefit them.  

Verse three continues, And hereby we do know that we know him, if we keep his commandments.  John then said we can know that we know God by keeping His commandments.  We cannot be saved by the Law of God, but if we are saved, we should keep His commandments because of our faith in Jesus Christ.  

Verse four states, He that saith, I know him, and keepeth not his commandments, is a liar, and the truth is not in him.  John went further here, saying that if we claimed to be saved by knowing Jesus Christ as our Savior and Lord but didn't keep His commandments that we are liars.  Salvation does not free us from obeying God's law, but it simply removes the death sentence when we do sin as long as we have truly put our faith in Him.  

Verse five adds, But whoso keepeth his word, in him verily is the love of God perfected: hereby know we that we are in him.  John said that anyone who kept God's law after being saved had the word of God perfected through what that person does.  He added that by keeping God's word that we can know that we are a part of God's kingdom.  Keeping the Law does not save us, but once we are saved, we should obey God's law.