A dogma is a teaching of the Church that has been proposed infallibly by the Magisterium as something that has been revealed by God. This means you are required to believe it and, if you deny it obstinately, you are a heretic, are outside of full communion with the Church, and your salvation is in jeopardy.
Even if your heresy is merely material and not formal (translation: you believe a heresy out of ignorance, not out of rebellion to the Church), in which case your salvation may not be jeopardy, heresy is still dangerous: it means you misunderstand something fundamental about the faith.
This can cause at least two problems: (1) Since all doctrine is systematic, believing one heresy will likely lead you to believe other heresies in order to be consistent. (2) Since orthopraxis (right action) is based off of orthodoxy (right belief), believing heresies can lead to sin or otherwise not living the fullness of the Christian life.
Here are three dogmas that, in my experience, many Catholics just don’t know about – and to their great loss:
1) Original Sin alone condemns a person to hell.
From the 6th Session of the Council of Florence: “We define…[that] the souls of those who depart this life in actual mortal sin, or in original sin alone, go down straightaway to hell to be punished, but with unequal pains.”
So do only people who have committed great sins and explicitly rejected God go to hell? No. Original Sin alone is enough to condemn a person to hell. And according to the Council of Trent, the stain of Original Sin is passed on by propagation: it’s a stain we have from the moment of our conception.
Baptism, or the desire thereof, applies the grace of Christ and is the only means of removing Original Sin (another dogma). This is why we baptize infants. Even though they are not capable of committing any sins personally, they have Original Sin and thus are in desperate need of the grace of Christ offered in baptism for their salvation. It’s also why many missionaries have given their lives to physically preach the Gospel to non-believers – and then baptize them.
Orthopraxis: Get baptized yourself if you aren’t already, get your children baptized, and evangelize any non-Christians you know so they can be baptized and have their Original Sin removed.
2) For those who have sinned mortally after baptism, the Sacrament of Confession, or the desire thereof, is necessary for salvation.
From the 14th Session of the Council of Trent: “[T]his sacrament of Penance is, for those who have fallen after baptism, necessary unto salvation; as baptism itself is for those who have not as yet been regenerated.”
A mortal sin is any sin that is regarding a grave matter and is carried out with both full knowledge that it is wrong and with full intentionality (not done accident). Any mortal sin, if left unforgiven before a person dies, condemns that person to hell.
Any mortal sins committed before baptism are removed at baptism (only relevant to adults being baptized, not infants). But mortal sins after baptism can only be removed with the Sacrament of Confession, or the desire to receive the Sacrament of Confession.
Since this is true for anyone who has been baptized, this is also true for Protestant Christians (who have been baptized). If you’re thinking, ‘But my Protestant friends of course don’t ever to go confession to a Catholic priest’, you are correct – it’s a problem for their spiritual life and an example of how heresy (even if held out of ignorance) can have serious ramifications. The 16th century Protestant Reformers led large groups of people out of the fullness of the Church and away from the Sacraments, and it’s a serious problem.
Orthopraxis: Go to confession regularly. Especially be sure to go if you think you’ve committed a mortal sin. Don’t put it off, it’s a serious matter. Talk to Protestant Christians you know about the faith, trying to lead them to the fullness of the faith in the Catholic Church so they can receive all of the Sacraments, including the Sacrament of Confession.
3) Subjection to the Pope is necessary for salvation.
From Pope Boniface VIII’s papal bull Unam sanctam: “[W]e declare, we proclaim, we define that it is absolutely necessary for salvation that every human creature be subject to the Roman Pontiff.”
This dogma was reaffirmed by the 11th Session of the Fifth Lateran Council: “[S]ince subjection to the Roman pontiff is necessary for salvation for all Christ’s faithful, as we are taught by the testimony of both sacred scripture and the holy fathers, and as is declared by the constitution of pope Boniface VIII of happy memory, also our predecessor, which begins Unam sanctam, we therefore… renew and give our approval to that constitution.”
The technical term for rejecting the Pope is “schism”: “Schism is the refusal of submission to the Supreme Pontiff or of communion with the members of the Church subject to him.” (CIC 751)
The bishop of Rome is the successor of St Peter the Apostle who was made by Jesus the head of the Apostolic college. As an essential part of the Church, anyone who rejects him rejects the Church, the Body of Christ, and thus Christ himself.
Again, you may be thinking, ‘My Protestant friends don’t follow the Pope’. Yes, and it’s a problem. The Protestant leaders that led people to break off from the Pope and thus the Catholic Church in the 16th century did something objectively very evil. Many Protestants today may reject the Pope out of ignorance (though only God knows a person’s heart), nonetheless, as Christians they should be consciously subject to him – and Catholics should help them do that.
Orthopraxis: Follow the teachings of the Pope and remain engaged in a parish headed by a priest who is in communion with a bishop who is in communion with the bishop of Rome. In other words, stay in the Catholic Church and try to lead others to the fullness of the Catholic Church as well.