When does God impute His righteousness to a believer?
God imputes His righteousness to a believer as soon as that person believes the Gospel with the heart, not merely with head knowledge. This believing is unto righteousness; the moment one trusts the message that Christ died for the world and for oneself, God clothes him with Christ's righteousness.
Les teaches that Romans 10:10 makes clear that righteousness is received by heart belief, not just head knowledge. He says we must examine whether we are believing with all our innermost being that Christ died for the world, for me. With the heart man believes unto righteousness, and this is an imputed thing: as soon as we believe the Gospel, God imputes His righteousness. Les connects this to Genesis, where God clothed Adam and Eve with coats of skins and clothed them with righteousness, and to Isaiah 61, where the garments of righteousness are mentioned. He also ties it to Romans 3, where Paul says this happens unto all that believe, so God can actually clothe the believer with the righteousness of Christ.
For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.