Justification is the most excellent work of God's love made manifest in Christ Jesus and granted by the Holy Spirit. It is the opinion of St. Augustine that "the justification of the wicked is a greater work than the creation of heaven and earth," because "heaven and earth will pass away but the salvation and justification of the elect . . . Will not pass away." He holds also that the justification of sinners surpasses the creation of the angels in justice, in that it bears witness to a greater mercy.
Source: Catechism of the Catholic Church (Vatican.va)