​Important Differences between Roman Catholic and Protestant Beliefs

Are good works necessary for salvation?

Roman Catholics believe that besides faith in Jesus Christ, good works are necessary for salvation.
"We can therefore hope in the glory of heaven promised by God to those who love him and do his will. In every circumstance, each one of us should hope, with the grace of God, to persevere to the end and to obtain the joy of heaven, as God's eternal reward for the good works accomplished with the grace of Christ." (Catechism of the Catholic Church)

Protestants believe that good works are not required for salvation. We are saved by faith alone.
For it is by grace you have been saved, through faith-- and this not from yourselves, it is the gift of God-- not by works, so that no one can boast. (Ephesians 2:8-9)

...he saved us, not because of righteous things we had done, but because of his mercy. (Titus 3:5)

Relying on faith alone for salvation does not mean that a Christian is not interested in doing good works. If a person truly believes God has saved him, he will want to do good to please God.

The Bible also tells us that if a person truly belongs to Jesus, God will transform his life supernaturally.(2 Corinthians 5:17) This means that if a person continues a life of sin deliberately, it indicates that he may not be truly saved and his faith may not be genuine. Like James said, if a man claims to have faith but does not have good works, his faith is not genuine and therefore cannot save him. (James 2:17)

In conclusion, a Christian does not do good works to earn himself eternal life in heaven. He does good works to show God that he loves Him. Good works are not a condition for salvation, they are the result of salvation and the natural consequence of a saved life.
 

Are works of penance necessary?

Roman Catholics believe that works of penance are required as some compensation to God for sins committed.
"…sin also injures and weakens the sinner himself, as well as his relationships with God and neighbor. … the sinner must still recover his full spiritual health by doing something more to make amends for the sin: he must make satisfaction for or expiate his sins. This satisfaction is also called penance." (Catechism of the Catholic Church)
Protestants believe that works of penance are not necessary for the remission of sins because the Bible teaches that when Christ died for our sins, He also paid for sin's penalty and satisfied God's divine justice completely. There is no need for us to continually offer sacrifices for our sins by works of penance.

 ...because by one sacrifice He has made perfect forever those who are being made holy. (Hebrews 10:14)
 When he had received the drink, Jesus said, "It is finished." With that, he bowed his head and gave up his spirit. (John 19:30)

 Since Christ has fully paid for the debt of our sins, all that is left for us to do in order to receive forgiveness of sins and escape condemnation is to have faith in Jesus.

All the prophets testify about him that everyone who believes in him receives forgiveness of sins through his name." (Acts 10:43)

Because what Jesus did on the cross for the believer is complete, Protestants do not believe that when a believer dies, he will still have to suffer for his sins in a temporal place called purgatory. The Bible teaches that when a believer dies, he returns immediately to God in heaven.

The time came when the beggar died and the angels carried him to Abraham's side. (Luke 16:22)
 

Should we pray to the saints or confess our sins to a priest?

Roman Catholics believe that saints who are in heaven intercede to God on our behalf. Since they have led better lives during their time on earth, they are more effective in their prayers. Therefore, it is good to invoke their help in obtaining benefits from God.

"Being more closely united to Christ, those who dwell in heaven .... do not cease to intercede with the Father for us, as they proffer the merits which they acquired on earth.... So by their fraternal concern is our weakness greatly helped." (Catechism of the Catholic Church)

Protestants do not believe that petitions to God should be made through the Saints. This is because the Saints, being mere creatures of God and not like God, cannot possibly listen to the many prayers addressed to them simultaneously in different countries, in different languages and many of them not expressed orally but only mentally. Only God, who is omnipresent (present everywhere) and omniscient (all-knowing) can do that. This applies to the Virgin Mary, who was although highly regarded by God and chosen to be the earthly mother of Jesus, was only a creature of God and unable to hear our prayers from heaven.

While we should not pray to a dead saint to intercede for us, Christians, while alive on earth, should pray and intercede for each other.

Similarly in the area of confession, one should not think that priests can assume the function reserved only for God. The Bible tells us to go direct to God to confess our sins.

Let the wicked forsake his way and the evil man his thoughts. Let him turn to the LORD, and he will have mercy on him, and to our God, for he will freely pardon. (Isaiah 55:7)

Even the Jews in Jesus' days understood that no one can forgive sins except God.

When Jesus saw their faith, he said, "Friend, your sins are forgiven." The Pharisees and the teachers of the law began thinking to themselves, "Who is this fellow who speaks blasphemy? Who can forgive sins but God alone?" (Luke 5:20­21)

While we should not pray to a dead saint to intercede for us, Christians, while alive on earth, should pray and intercede for each other.