What Justification by Faith really is !
First of all, Justification by Faith cant apply to #1. The unregenerate, because Faith is a Spiritual Fruit 5:22
22 the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith
Now, man may have faith which is the fruit of the flesh, a natural human faith, but that has nothing to do with Justification.
#2. Justification by Faith cant apply to the unjustified, in other words, one must already be Justified before God before they can be Justified by Faith.
Justification by Faith is when one who has been Justified by the Blood of Christ alone and before God based on Christ's Blood Rom 5:9 when they receive a conscience assurance of it by Faith the fruit of the Spirit.
Faith justifies the conscience with the spiritual knowledge of the imputed righteousness of Christ . God purifies our hearts by Faith Acts 15:8-9
8And God, which knoweth the hearts, bare them witness, giving them the Holy Ghost, even as he did unto us;
9 And put no difference between us and them, purifying their hearts by faith.
The word heart here does include the conscience, for its the word kardia and means:
lit: the heart; mind, character, inner self, will, intention, center.
kardía – heart; "the affective center of our being" and the capacity of moral preference
Faith gives us assurance of our Justification as in the full assurance of Faith Heb 10:22
Let us draw near with a true heart in full assurance of faith, having our hearts sprinkled from an evil conscience, and our bodies washed with pure water.
Justification by Faith Rom 5:1 is again conscience Justification, wherein the conscience is given to know the peace it has with God, and so its the peace of believing Rom 15:13
Now the God of hope fill you with all joy and peace in believing, that ye may abound in hope, through the power of the Holy Ghost.