2 Timothy 2:19 says, 'Let everyone who names the name of Christ depart from iniquity.' Every person who is born again (John 3:5; Acts 2:38) must depart from iniquity. This may not happen instantly, however. God is patient and allows each of us time to grow in grace and holiness. But if a person shows no desire to depart from iniquity but seems to accept his addiction, then he will eventually fall from grace. Hebrews 6:4 could apply to such a person, but keep in mind that it is not saying a person cannot be forgiven; it's saying that a person cannot repent so long as he is rejecting the One who grants repentance.