ONE OF THE main heretical teachings of Protestantism is sola fide (by faith alone). It says that our salvation rests on faith alone--we are saved by faith alone--and good works have nothing to do with. As a corollary, it insists that good works are mere "fruits" of our being saved, and cannot help us inherit Heaven because believing on Christ sacrifice in the cross is enough to bring us to Heaven.
Since Protestantism does not believe in sanctifying grace (the grace that makes us holy), Protestants believe salvation as purely justification of personal sins. They have no notion with regards to the loss of the sanctifying grace as a consequence of the rebellion of our primordial parents Adam and Eve when they disobeyed one law of God not to eat the fruit of the tree of good and evil in the Garden of Eden. Thus their understanding of "justification" is the wiping of all personal sins in the sacrifice of the Cross, and any sins thereafter are automatically wiped as an effect of that "justification" without need of any need of sacramental act in seeking forgiveness through confession and the sacrament of reconciliation. This understandinf of "justification" make them tend to believe that any sins they commit after their Protestant baptism has no eternal consequence for them simply because they have already been "justified."
Inheriting Heaven Arises from Doing Works of Mercy
One evidence that stands against the Sola Fide Heresy comes from the Gospel of Saint Matthew. Jesus taught his disciples: "Then the king will say to those on his right... Inherit the kingdom prepared for you from the foundation of the world. For I was hungry and you gave me food; I was thirsty and you gave me drink; a stranger and you welcomed me, naked and you clothed me, ill and you cared for me, in prison and you visited me" (25: 31-46).
The Lord makes it clear that we will inherit the kingdom of Heaven because he was hungry and we gave him food, thirsty and gave him drink, a stranger and we welcomed him, naked and we clothed him, ill and we cared for him, in prison and we visited him. It is a clear action and consequence statement. The action (you did it to me) resulted into a positive consequence (inheriting the kingdom of Heaven).
Even Saint Paul counselled the Christians in Philippi: "Work for you salvation in fear and trembling" (Philippians 2.12: The Jerusalem Bible).
Protestants will have difficulty accepting this teaching--that explains why they rarely, if at all, quote these New Testament passages when teaching about salvation. The teaching simply opposed the Protestant teaching of "by faith alone."
But Catholics have no problem in understanding this teaching of the Lord. Our teaching on the sanctifying grace put us consistently with this teaching of Christ as recounted by the Apostle Saint Matthew, the first bishop of Jerusalem. We know that our salvation, or sanctification, has not been a result of the wiping of our sins through baptism, but founded on the restoration of the sanctifying grace into our soul by the sacrifice on the Cross. We were made holy (sanctified, or justified); but that does not free us from the responsibility and consequences of our personal sins later on. We believe that we can loss our salvation because of our unrepented personal sins as well as "inherit the kingdom of God" by the good works we continue to do.
Thus we seek forgiveness for our personal sins after Baptism in order to reconcile ourselves with God on the acts of evil that we committed and wipe these transgression through confession and absolution by the priestly order to whom the apostles transmitted their authority to forgive and not forgive sins, an authority that the Lord himself has given to the Twelve.
While we are restored in good graces with God, that does not end it all. We still have to live that sanctification until the day we die. Along the way we can loss Heaven through our personal sins unforgiven.
[This section quotes from the New American Bible.]

