Habitual Sin

Keep your servant from deliberate sins! Don’t let them control me. Then I will be free of guilt and innocent of great sin. (‭Psalms‬ ‭19‬:‭13‬ NLT)

Habitual sin is of grave concern because it is a reflection of the heart. 

When a child of God sins, they will feel anguish over that sin because they know they have saddened the heart of God.  This should lead to repentance and a true desire to turn away from that sin. 
To be in a pattern of habitual sin, to be living a sinful lifestyle, indicates that we are feeling less and less anguish over our sin and less and less of a desire to make a change. 
Suddenly we find that we have chosen our sin (whatever that may be) over our relationship with Christ. Scary!