It is in Christ that we are justified (Acts 13.39; Romans 8.1; First Corinthians 6.11; Galatians 2.17). At the outset we are here advised that it is by union with Christ and by some specific relation to him involved in that union that we are justified
(p. 126, 127)
See also: Ridderbos on the justification of the ungodly in union with Christ.