Two quotes from Calvin on Union with Christ (or Unio Mystica):

First, we must understand that as long as Christ remains outside of us, and we are separated from him, all that he has suffered and done for the salvation of the human race remains useless and of no value for us. Therefore, to share with us what he has received from the Father, he had to become ours and to dwell within us.

— Institutes III. 1. 1 cited by Charles Partee, The Theology of John Calvin, 40

Therefore, that joining together of Head and members, that indwelling of Christ in our hearts — in short, that mystical union — are accorded by us the highest degree of importance. We do not, therefore, contemplate him outside ourselves from afar in order that his righteousness may be imputed to us but because we put on Christ and are engrafted into his body — in short because he deigns to make us one with him.

Institutes II. 16. 19 cited by Charles Partee, The Theology of John Calvin, 41

Both of these quotes illustrate something that stands at the heart of an ‘Evangelical’ approach to Calvinism; and that is the vicarious life of Christ. If we aren’t ‘really’ brought into His life, in the Incarnation and Atonement (both of these being inextricably linked), then salvation only ends up dealing with the symptoms (murders, lying, stealing, lusting, blaspheming, etc.) — the external problems — and not with the “heart problem” (where the murders, lying, etc. flow from). If Jesus didn’t get into our skin, and thus we into His, then we end up with a half baked salvation . . . which really is no salvation. More to come . . .