Kevin, (continued)
Even though one who believes and is perfectly contrite for his or her sins receives the grace of justification in that moment, even before receiving the appropriate sacrament, this grace is only provisional, and is granted only in view of the anticipated Sacrament of Penance: a sinner who had no intention of receiving this sacrament would clearly be lacking in either faith or repentance, and so would not be justified. Those who believe and repent, but are less than perfectly contrite for their sins, are not justified until the moment they receive the Sacrament of Penance, which imparts the further grace which they need.

Kevin, the humble tax collector went home a changed man after admitting His sinfulness loud before God. (Like we do when we confess to Jesus' servant, the Priest in the Sacrament of Penance.) This man knew not only that he was a sinner, but knew/trusted/believed that God was the only one who could deliver him from the power and practice of sin.