Updated: Aug 14, 2021
By Luke Lancaster
One of the key differences between Protestant-Christians and Catholic-Christians is the understanding of mortal sin. Catholics believe the biblical teaching that they can lose Heaven or salvation by committing a serious sin. This teaching can be seen in John’s Gospel, where Jesus gave the analogy of the vine and the branches. The branches remain attached to the vine by obeying Jesus's command to love (John 15:10, 12). Branches can be broken off from the vine (John 15:6), and this happens when one stops abiding in the vine. Lacking charity in a grave manner is a mortal sin.
In one of the parables, Jesus said, "I am the vine; you are the branches" (Jn. 15:5). Every Christian needs to “remain” or “abide” in Christ, as every branch needs to stay attached to the vine to stay alive (15:4). This is the way to eternal salvation: living in Christ. He clarifies: “If you keep my commandments, you will abide in my love" (15:10). To be a living Christian destined for heaven, he or she needs to obey Christ's commandment. The question is then asked, "what is that commandment?"
The commandment which determines whether somebody is attached to Christ or not is love. Jesus said, "This is my commandment, that you love one another as I have loved you" (John 15:12). Loving other people like Christ is how Christians remain attached to the vine. This is so serious in Christ’s mind that He boldly proclaimed: “If anyone does not abide in me he is thrown away like a branch and withers; and the branches are gathered, thrown into the fire, and burned.” (15:6). Branches don't survive fire. So, this fire isn't likely temporary, but referring to Hell (such as Mt. 25:41). If Christians seriously disobey Christ’s commandment to love, he or she is broken off from Christ and goes to Hell.
Jesus taught mortal sin in John 15. This is not only apparent to Catholics, but some Protestants as well. Protestant Scripture scholar I. Howard Marshall said that John 15 is a “warning [to] disciples who disobey Christ that they may cut themselves off from him” (New Testament Theology, p. 508). Christians can lose their salvation and become separated from Christ due to their actions.
Some may object and say that Jesus could not possibly mean this, for no Christian can love perfectly. While true, there is a distinction called mortal sin and venial sin. The former is a sin that deserves “a severe beating,” and the latter is a sin that deserves “a light beating” (Luke 12:47-48). To sin mortally against charity deserves the severe beating of hell, and cuts the branch from the vine. To sin venially or lightly against charity deserves a light beating of punishment.
Mortal sin is a reality for Christians. To claim that it is not would contradict John 15. Christians are not eternally secure and destined for heaven. Hell is a possibility. Just as a branch can get snipped off of a vine (such as the Jews who rejected the Messiah, Romans 11:22), so also Christians can get "severed" from Christ (Galatians 5:4).