“What are the implications of union with Christ? In essence this:
Through our union with Him in His death we are set free from the penalty of our guilt, which He has paid for us;
In union with Him in His resurrection a complete, final, and irreversible righteousness is ours;
In union with Him in His death and resurrection we have been set free from the reign of sin.
Yet we remain sinners in ourselves. Sin continues to indwell us;
Only when our regeneration comes to further flowering beyond this life will we be free from sin’s presence.
These distinctions are vital. While guilt is gone and the reign of sin has ended, sin continues to indwell us and to beset us.
It still has the potential to deceive us and to allure us. Once we understand this, we will not confuse the ongoing presence of sin with the absence of new life in us.
Without that stability in our understanding, our assurance will be liable to ebb and flow.”
–Sinclair B. Ferguson, The Whole Christ: Legalism, Antinomianism, and Gospel Assurance—Why the Marrow Controversy Still Matters (Wheaton, IL: Crossway, 2016), 218–219.