First of all, I believe that the body of Christ is not divided into Protestants and Catholics and I believe there are born-again followers of Jesus in both camps. Paul makes it clear that this kind of division in the body of Christ is not good.
What I mean is that each one of you says, “I follow Paul,” or “I follow Apollos,” or “I follow Cephas,” or “I follow Christ.” Is Christ divided? Was Paul crucified for you? Or were you baptized in the name of Paul?
(1. Corinthians 1:12-13)
So can I have fellowship with someone who claims to be Catholic? If the person is born again and follows Jesus, it does not matter if he is Catholic or Protestant; we can enjoy spiritual fellowship. Why? Because we are part of the same body and under the same authority (head).
The issue to ask is not what kind of denomination people are from, but if they are part of the body of Christ; or in others words if they are Christian. Christianity is properly defined by certain doctrines that are revealed in the Bible and they are as follows:
- There is only one God, and you are to serve no other gods or worship images made by human hand
(Exodus 20:3; Isaiah 43:10; 44:6, 8).
- Jesus is both God and man
(John 1:1, 14; 8:24; Col. 2:9; 1 John 4:1-4).
- Jesus died on the cross for the sins of the world and rose from the dead physically
(John 2:19-21; 1 Cor. 15:14).
- Salvation is by grace through faith
(Rom. 5:1; Eph. 2:8-9; Gal. 3:1-2; 5:1-4).
- The gospel is the death, burial, and resurrection of Jesus according to the scriptures
(1 Cor. 15:1-4; Gal. 1:8-9).
- God is a Trinity
(Matt. 28:19; 1 Cor. 12:4-6; 2 Cor. 13:14).
- Jesus was born of the virgin Mary
So, someone who is a true Christian will believe these things. Catholics believe most of them, but not exactly the first and the fourth point. The clearest example is, for instance, that they practice prayer to Mary and other humans they have declared to be “saints”. In Roman Catholicism, they say that Mary is the mediatrix (Catechism of the Catholic Church paragraph 969); Mary made atonement for the sins of man (Fundamentals of Catholic Dogma, page 213); Mary is the subject of preaching and worship (Vatican Council II, p. 420); etc.
What’s more, Catholicism violates the biblical doctrine of salvation by grace through faith alone. This was Martin Luther’s big revelation and we should not forget that he was martyred with condolence from the official church for having this view. The Catholic doctrine says:
"If any one saith, that by faith alone the impious is justified; in such wise as to mean, that nothing else is required to co-operate in order to the obtaining the grace of Justification, and that it is not in any way necessary, that he be prepared and disposed by the movement of his own will; let him be anathema (cursed)“ (Council of Trent, Canons on Justification, Canon 9).
One might say that we are not that different, which is to some extent true. Most of the Catholic beliefs are the same as Christian beliefs, but if you want to have fellowship with Catholics, you need to ask yourself how important some points are to you.
- How strongly do you disagree when it comes to praying and worshipping humans?
- How strongly do you disagree that faith is not enough for salvation?
- How strongly do you disagree with direct worship of the physical bread in communion?
- How strongly do you disagree with Jesus not being the only mediator between God and man?
- How strongly do you disagree with the teaching that there is a purgatory?
- How strongly do you disagree with the teaching that you can pay somebody out of that purgatory?
- How strongly do you disagree with the teaching that Mary also paid atonement for our sins?
If these are just minor points that do not hold an essential place in your doctrine, then you will have no problems working together with the Catholic church or viewing Catholics as Christians. But if you consider these points to be essential to the Christian faith, then you would have problems with the Catholic church; because they are not going to change their beliefs on these issues.