Dr. Robert Preus is known for advocating UOJ in the 1980s, when Concordia Seminary in Ft. Wayne was also deep into Church Growth Enthusiasm. In his last book, edited after his death by his sons Daniel and Rolf, his clear stance against UOJ is obvious.
When does the imputation of Christ’s righteousness take place? It did not take place when Christ, by doing and suffering, finished the work of atonement and reconciled the world to God. Then and there, when the sins of the world were imputed to Him and He took them, Christ became our righteousness and procured for us remission of sin, justification, and eternal life. “By thus making satisfaction He procured and merited (acquisivit et promeruit) for each and every man remission of all sins, exemption from all punishments of sin, grace and peace with God, eternal righteousness and salvation.”
But the imputation of Christ's righteousness to the sinner takes place when the Holy Spirit brings him to faith through Baptism and the Word of the Gospel. Our sins were imputed to Christ at His suffering and death, imputed objectively after He, by His active and passive obedience, fulfilled and procured all righteousness for us. But the imputation of His righteousness to us takes place when we are brought to faith.
Quenstedt says, It is not the same thing to say, “Christ’s righteousness is imputed to us” and to say “Christ is our righteousness.” For the imputation did not take place when Christ became our righteousness. The righteousness of Christ is the effect of His office. The imputation is the application of the effect of His office. The one, however, does not do away with the other. Christ is our righteousness effectively when He justifies us. His righteousness is ours objectively because our faith rests in Him. His righteousness is ours formally in that His righteousness is imputed to us.
Preus quoted this statement from Calov with approval, which is worth repeating -
Although Christ has acquired for us the remission of sins, justification, and sonship, God just the same does not justify us prior to our faith. Nor do we become God's children in Christ in such a way that justification in the mind of God takes place before we believe.
 "In an initial burst of enthusiasm reflecting Preus's concern for missions, the Fort Wayne faculty had petitioned the 1977 convention of the Missouri Synod to have each of its subdivisions or districts ‘make a thorough study of the Church Growth materials.’ What is more, the districts were to be urged to ‘organize, equip, and place into action all of the Church Growth principles as needed in the evangelization of our nation and the world under the norms of the Scriptures and the Lutheran Confessions.’ By the time of the 1986 synodical convention, however, the same faculty, while appreciating the ‘valuable lessons of common sense’ to be learned from Church Growth, asked that ‘the Synod warn against the Arminian and charismatic nature of the church-growth movement.’ Kurt E. Marquart, "Robert D. Preus," Handbook of Evangelical Theologians, ed., Walter A. Elwell, Grand Rapids: Baker Book House, 1995, pp. 353-65. Reprinted in Christian News, 6-26-95, p. 21.
 R. Preus footnote: Systema, Par. II, Cap.3, Memb. 2 S. 1, Th. 44 (II, 363). Cf. Abraham Calov, Apodixis Articulorum Fidei (Lueneburg, 1684), 249: “Although Christ has acquired for us the remission of sins, justification, and sonship, God just the same does not justify us prior to our faith. Nor do we become God’s children in Christ in such a way that justification in the mind of God takes place before we believe.” Justification and Rome, footnote 74, p. 131.
 Robert D. Preus Justification and Rome, St. Louis: Concordia Academic Press 1997, p. 72.
 Systema, Par. III, Cap. 8, S. 2, q. 5, Observatio 19 (II, 787). R. Preus footnote #76, Justification and Rome, p. 132.
 Apodixis Articulorum Fidei, Lueneburg, 1684. Cited in Robert D. Preus, Justification and Rome, St. Louis: Concordia Academic Press 1997, p. 131n.