The first work of the grace of the Holy Spirit is conversion, effecting justification in accordance with Jesus' proclamation at the beginning of the Gospel: "Repent, for the kingdom of heaven is at hand." Moved by grace, man turns toward God and away from sin, thus accepting forgiveness and righteousness from on high. "Justification is not only the remission of sins, but also the sanctification and renewal of the interior man.
Source: Catechism of the Catholic Church (Vatican.va)