The forensic (i.e. justification) and the transformative (i.e. sanctification) are a manifestation of our relation to Christ. Both justification and sanctification are aspects of our union with Christ; that is to say Christ ‘in us’ is Christ ‘for us’. Christ’s significance to the believer is forensic and transforming. Consider what Owen and Goodwin have to say on this issue:
“Union with Christ”, says Owen, “is the principle and measure of all spiritual enjoyments and expectations” (21:146) .
And hence is our justification: for … being united unto Christ, we are interested in that acquitment from the condemning sentence of the law which was granted unto himself when he satisfied it to the utmost …. Our union with him is the ground of the actual imputation of his righteousness unto us; for he covers only the members of his own body … (21:150).
What did Goodwin have to say? All of God’s justifying acts toward us “depend upon union with Christ, we having him, and being in him first, and then thereby having right to his righteousness …” (8:406)
(HT: Thomas Goodwin)