The two most important doctrines that must be shared when witnessing to Roman Catholics are: 1) the supreme authority of God's Word and 2) the sufficiency of Jesus Christ. Catholics are taught that their religious traditions (which have evolved over the last 1600 years), and the "infallible" teaching authority of the Magesterium (bishops), are equal in authority to God's Word. Yet there is no higher authority than almighty God. He has established His Word as the supreme and infallible standard by which all teachings and traditions of men are to be tested for veracity (Acts 17:11; Psalm 119; Mark 7:7-14). The fallible teachings of men must surrender tho the infallible Word of God. God's Word is sufficient for salvation. Scripture is able to make us wise for salvation through faith in Christ Jesus (2 Tim. 3:15).

Roman Catholics deny the sufficiency of Jesus Christ in salvation. In fact, they deny or reject all the Scriptures that prove He is sufficient to save sinners completely and forever. Catholics deny "He is able to save to the uttermost those who draw near to God through him, since He always lives to make intercession for them" (Heb. 7:25). They are taught they must do their part because Jesus did not do it all. They also deny all the following verses which declare His sufficiency.

He saves forever 
"I give them eternal life, and they will never perish, and no one will snatch them out of my hand" (John 10:28). Catholics do not have eternal life, only conditional life which is based on what they do to maintain their salvation. 

He obtained eternal redemption 
"In him we have redemption through his blood, the forgiveness of our trespasses, according to the riches of his grace" (Eph. 1:7). Catholics are taught the work of their redemption continues on their altars every day.

He cancelled and forgave the entire sin debt 
"God made alive together with him, having forgiven us all our trespasses by canceling the record of debt that stood against us with its legal demands." (Col. 2:13-14). Catholics need to confess their mortal sins to a priest and do penance to be forgiven. 

He purifies all sins
If we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus his Son cleanses us from all sin (1 John 1:7). Catholics are taught purgatory is a cleansing fire that purifies their sins. 

He redeems from the curse of the law
"Christ redeemed us from the curse of the law by becoming a curse for us" (Gal. 3:13). Catholics must obey the law to be saved. 

He is the only sinless mediator (1 Tim. 2:5)
"There is one God, and there is one mediator between God and men, the man Christ Jesus" (1 Tim. 2:5). Catholics are taught Mary is another sinless mediator.

He is the only way 
Jesus said to him, "I am the way, and the truth, and the life. No one comes to the Father except through me (John 14:6). The pope says atheists can follow their hearts into heaven.

He provides a permanent right standing before God.
"By a single offering he has perfected for all time those who are being sanctified (Heb. 10:14). Catholics lose their justification when they commit a mortal sin and must be rejustified by the sacraments. 

He gives every spiritual blessing 
"Blessed be the God and Father of our Lord Jesus Christ, who has blessed us in Christ with every spiritual blessing in the heavenly places" (Eph. 1:3). Catholics who believe the false and fatal gospel of Rome are void of blessings and destined to the eternal punishment of hell unless they repent and believe the true Gospel of grace. 

When we witness to Catholics we must show them the true Jesus Christ who is revealed so majestically and gloriously in God's supreme authority for truth - His Holy Word!