As mentioned earlier in this space the older Reformed writers had a doctrine of forensic holiness or sanctification but rather than connecting it with union with Christ considered logically prior regeneration and faith, they tended to connect talk about it under the application of redemption. This passage from Caspar Olevianus’ Expositio Symboli Apolostolici (1576) is typical enough:

The church is holy in two ways, by renewal and by imputation (John 13 [:10]).  By renewal in itself, such holiness has only begun (Romans 7 [:13-25]).  Regarding this first kind of holiness, 2 Corinthians 7 [:1] says, “Perfecting your sanctification” (see also 1 Thessalonians 4 [:7]).  But by imputation the church’s holiness is most perfect in Christ, as he says [John 17:19]: “For their sakes I sanctify Myself.”  In this second kind of holiness I believe that there is no sin and death in the church, that is, that no blame or punishment is imputed to true members of the church.  For those who believe in Christ are not sinners and not liable to death.  Rather, they are unconditionally holy and righteous, lords in Christ over sin and death, and those who live forever (Romans 5:8-9; Hebrews 10:14; Colossians 2:10; Romans 8:1; 1 Thessalonians 5:10).

For Olevianus, there was no such forensic holiness prior to faith in Christ. This passage occurs near the end of the treatise, in his discussion of the fourth part of the Creed: “Credo sanctam Ecclesiam catholicam, sanctorum communionem.” The logic of the section is thus: Sanctity, like justification, comes through faith alone and the Spirit creates faith through the preaching of the gospel and the preaching of the gospel occurs in the visible church.

A second thing to observe in this brief passage is that Olevianus did not set progressive sanctification over against the forensic aspect of sanctification. This was fairly typical of most of the mainstream of Reformed theology. There are realistic elements (e.g., the transmission of corruption) alongside and complementary to the forensic doctrines of the imputation of sin and the imputation of righteousness. The one need not obviate or obliterate the other.