A question I got via email. Nicely, it was given as a multiple-choice. But, as usual, I answered it with an essay:
Is suicide something that
a. shows that you are actually not a true Christian.
b. makes you lose your salvation.
First, you have to ask whether sin in general can make you lose your salvation. I would say it could, if you have a lifestyle issue that you do not repent of-- that would be Hebrews 10:26-27.
But is suicide a sin? My short answer is: it depends.
Suicide is rarely mentioned in Scripture. First of all, in a sense, Jesus' death was a suicide because he could have prevented his death many times, but refused to do so. To "willingly" go to death, as is mentioned of many martyrs, is a form of suicide.
And suicide is never mentioned in Scripture as a sin.
However, there are lots of issues here. First of all, what is the motivation for suicide? If a person is committing suicide because they "just can't take life anymore" then there are two ways to work it-- either they are a "coward" and so won't enter the kingdom because Rev. 21:8 says they won't, or they are depressed and not thinking clearly and so, ultimately they are sick and perhaps will be forgiven under God's mercy.
I had one friend of mine in high school who committed suicide and she left a note saying, "I just want to be with Jesus." So, rather than giving up faith, she actually committed suicide in faith and because of her faith, as misguided as it was.
Another aspect of suicide is loving others. A suicide is usually convinced that no one cares about them and they are almost always wrong. So their suicide harms a number of people, which goes against the basic law, "Love your neighbor as yourself." But, suppose the suicide is convinced that their death would bring a benefit-- like Jesus' did-- and so they think-- wrongly, usually-- that they are loving people by taking their life? Then wouldn't it be a righteousness on their part instead of a sin?
Is suicide an unpardonable sin? No, there's only one of those and Jesus says it is blasphemy of the Holy Spirit. Suicide is not that, so it can be forgiven.
So I think suicide depends on the motivation, which is almost impossible for us to guess on this side of eternity. So, for the believer who commits suicide, all we can do is pray for God's mercy on them, and give them to His hands.
One last thing: The early church never declared suicides sinners because they saw the connection between martyrdom and suicide. Augustine, in the fourth century, is the first one to declare suicide a sin, and he said it was because suicide is a sign of despair, which is the opposite of faith. But that isn't always true. The Catholic church, in determining that suicide is an unpardonable sin uses the same logic, but, again I think they're wrong about that.