"No one who lives in him keeps on sinning. No one who continues to sin has either seen him or known him." NIV translation
If you are in Christ, sin will not control you and you will not make a lifestyle of it. We still commit sins but we do not live in the sin and are not happy and content with the sin. The good news is that God has given us the power through the Holy Spirit to live a holy life.
"Dear children, do not let anyone lead you astray. He who does what is right is righteous, just as he is righteous. He who does what is sinful is of the devil, because the devil has been sinning from the beginning. The reason the Son of God appeared was to destroy the devil's work." NIV translation
As children of God, we will seek to be like Jesus and that means we will do the right things. Those who are not children of God will live in sin just as the devil has from the beginning. The good news is that Jesus came and brought us victory over the work of Satan.
"No one who is born of God will continue to sin, because God's seed remains in him; he cannot go on sinning, because he has been born of God." NIV translation
If you are saved, then you have God living in you through the Holy Spirit. The Spirit will not allow you to be at peace and still living in a pattern of sin. We all will commit sins but living happily in a lifestyle of sin is a clear warning sign that the Spirit is not in control of your life.
"This is how we know who the children of God are and who the children of the devil are: Anyone who does not do what is right is not a child of God; nor is anyone who does not love his brother." NIV translation
As we see here, we are not all children of God. To be a child of God you must accept Jesus Christ as your Lord and Savior. If you are a child of God, people will be able to tell it. You will try to be like Jesus as you were called to be His disciple and so you will do what is right. You will also be known by your love for others because God is love and He lives in you.