Participatory, Forensic, and Renovative
The basic unio-duplex gratia structure of his applied soteriology is such that the participatory (union) has both forensic (justifying) and nonforensic (sanctifying, renovative) dimensions or aspects, without any confusion or interpenetration of these two aspects. To view union/the participatory as introducing, by imputation, a nonforensic and so presumably Spirit-worked element into an otherwise forensic justification is to blur a basic distinction that Calvin was intent on maintaining, a blurring, further, that he would see as undermining the stability of a fully gracious justification.
Richard Gaffin, Justification and Union with Christ, Theological Guide to Calvin's Institutes, pg. 262