One of the central tenets of Christian counselling is the putting off of the old self and putting on of the new (Ephesians 4:22-24). Most of our behavioural failures stem from the old self, with its ingrained patterns of sin. Recognising these patterns and dealing with them is essential for healthy, godly lives and relationships.
The struggle to continue to grow in the likeness of the new self beyond what seems to be a natural limit is also one of the chief problems with Christians who hold a neonomian doctrine, the mixing of justification and sanctification. The process of putting off the old is rapid for many new Christians but becomes increasingly difficult as we achieve a greater refinement of character. Slip ups, backsliding and new patterns of sin which appear at different times and for varying periods can produce a great sadness and lack of assurance for neonomians.
Hoatius Bonar helpfully clarifies the distinction between the old man and the new based on Romans 7. It is not that the old and new are two persons, as we are each only one person, but that each believer has both a legal condition and a moral state:
This mysticism as to the old and new man proceeds on a confusion similar to that which mixes up justification and sanctification. The “old man,” in the apostle’s figure, evidently means sometimes our former legal condition, and at other times our former moral state. In the first sense, the old man is “crucified,” put off” once for all, in believing, when we cease to have “confidence in the flesh” (Phil 3:3). Thus far it is true that it is not amended, but set aside entirely. In the second sense, there is a daily putting off what is old, and putting on what is new. It is like our putting on Christ, which is done once for all at justification, but also gradually, in the process of renewing, so that in one place we read, “Ye.. have put on Christ” (Gal 3:27), and in another, “Put ye on the Lord Jesus Christ” (Rom 13:14). The mixture of these two things is the chief source of the errors we have been exposing.
For further notes on this subject see my post called spot the difference?