The word "justification" has many uses, but the most prevalent I've seen is as ego's excuse.
I feel justification or "reasonableness" every time I remain attached to something through ego (self-righteousness) and ignore God.
Such attachments can be driven by fear -- fear of being made wrong, fear of failure, fear of losing what is comfortable or familiar, fear of physical discomfort or pain. When I remember who I truly am -- a child of God without physical form, then all fear melts away. All reasonableness or justification why I'm not doing as God commands falls to the side.
Justification or reason is the lazy tool of ego. If you put love of God first, then one does not need a reason to follow the Law; it becomes the natural thing to do.