Concise Bible Dictionary:
Imputation has an important place in God’s plan of salvation. “Blessed is the man unto whom the Lord imputeth not iniquity” (Psa. 32:2; Rom. 4:8). The sins of the man believing on Jesus are not imputed to him: Christ has atoned for them; the believer may come under discipline for them (compare 1 Cor. 11:31-32; Hebrews 12:7), but there is no imputation. On the contrary, he enters into the blessedness of the man to whom God imputes, or reckons, righteousness without works. Abraham believed God and it was reckoned (same word) to him as righteousness; and this is true of believers generally (Rom. 4:3-4). Therefore not only are the believer’s sins not imputed to him; but he is accounted righteous.
In 2 Corinthians 5:19 the aspect in which Christ came to earth was that of grace. God was in Christ reconciling the world to Himself, and not imputing to men their offenses; but, alas, they refused the grace, and put Him to death. In Romans 5:13 the word is ἐλλογέω, “sin is not put to account when there is no law.” It is sin, and those that sin without law perish without law; but they are not at once called to account for it in God’s government (compare Acts 17:30).