Is that a personal belief, or do you have Scriptural backing?
It mentions nowhere in the Bible that suicide is sin. In fact, there is only about five different instances of suicide mentioned in the Bible, and not once is eternal punishment listed as a result.
The belief came from St. Augustine's postulation (which obviously draws heavily on Catholic dogma) that killing yourself is 'self-murder', and thus as murder is a sin, so is this. And due to the idea of the last rites, if you die without confessing your sin (as you would in suicide, as you're dead and can't repent) then you are sent to hell.
It's an interpretation, but nowhere does it say "suicide means hell."
Killing yourself is self-murder. If it isn't, then what is it? The forgiveness of sins doesn't work that way, that you have to mentally repent for each one, so you're right, it doesn't have anything to do with not being able to repent it.
Suicide isn't something you just decide to do. It isn't something you do for fun when you're bored. Committing suicide requires much mental preparation. The Bible lists characteristics of unsaved people:
- idolatry
- adultery
- prostitution
- theft
- greed
- drunkenness
- swindling
- impurity
- witchcraft
- discord
- jealousy
- fits of rage
- dissensions
- envy
- orgies
- lying
- cowardice
- unbelief
- sorcery
- sexual immorality
- homosexual offenses
- slander
- hatred
- selfish ambition
- murder
The Bible also lists characteristics of saved people:
- love
- joy
- peace
- patience
- kindness
- goodness
- faithfulness
- gentleness
- self-control
Now do you think thoughts of suicide come from things like love, joy, patience, and self-control? No, of course not. You're right and I agree that the Bible doesn't explicitly state that committing suicide will send you to hell, in fact the only relevant issue on salvation is faith in Christ. However, the results that the Holy Spirit brings about in a believers life is very clear. Suicide comes from evil thoughts over an extended period of time, since it isn't something you do on a whim, so anyone who is saved won't have extended periods of time of these evil thoughts of hopelessness, selfish ambition, cowardice, etc. Anyone who commits suicide while claiming they have faith in Christ is only fooling themselves.