Because of the serious nature of this question, I will be adding a teaching concerning this subject to the Chaplain's Page. Thanks for asking it; I hope the answer below helps other readers understand a complex subject. Please be aware that I have only touched the surface of this subject.
"Do not be afraid of those who can kill the body, but cannot kill the soul. Rather be afraid of the One who can destroy both soul and body in hell." Matt. 10:28
The bottom line concern of most people regarding suicide is "Fear, that in a moment's madness, we can somehow move ourselves out of God's sphere of influence & lose our salvation." Read the following quote (I thought this person said it very well.)
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(Quote)
"…the first thing to consider with this question is, did the person get right with God and live right for God before they died? People do not make it to heaven, regardless of how they died, if they had not yet accepted Jesus Christ as their personal Savior. That is, suicide is not the issue regarding whether a person goes to heaven. Getting right with God is the issue.."
"…it should be clear that although suicide is wrong, the essential issue regarding going to heaven is getting right with God before you die.
Incidentally, this does not mean that someone who wants to end the pain in their lives can get “fire insurance” by getting right with God before killing themselves. In such a case, it is obvious that the person’s real reason for getting right with God is not establishing a relationship with Him, but rather going through a procedure to “get the best deal.” Such a phony “acceptance” of God will not count. The following passage is relevant:
Galatians chapter 6
7 Do not be deceived, God is not mocked; for whatever a man sows, that he will also reap.
8 For he who sows to his flesh will of the flesh reap corruption, but he who sows to the Spirit will of the Spirit reap everlasting life.
Remember, the concept of “getting right with God” is to be adopted (through Jesus) into God’s family. How would you feel if you adopted someone who then committed suicide, leaving a note stating, “thanks for adopting me, I wanted to commit suicide and I am glad that I found someone who would pay for my funeral?” The reality is that you would then know that the person you adopted was only an opportunist—not someone interested in being part of your family. The point is that people who honestly want to get right with God are safe in His Hands. Those who have an ulterior motive to “have a relationship” with Him do not have that advantage."
Many times, a person who commits suicide is in a state of rebellion and angry. They opt for a permanent solution to a temporary problem & commit the greatest act of revenge they could imagine. "I'm hurting & I am not getting the attention I think I deserve, therefore I will kill myself and show them…" Suicide is NOT an option, especially for a believer. It will not keep a believer out of heaven, but it is an extremely poor witness to those left behind and it will place you in the presence of the King of Kings full of shame.
"And now, dear children, continue in Him, so that when He appears we may be confident and unashamed before Him at His coming." I Jn. 2:28
As a believer, I myself reached a state of depression where I did not see the point of continuing on and actually planned to commit suicide (I did not tell anyone about it) but the Lord Himself intervened and spoke to me to read Ecclesiastes. There I discovered someone else who felt the same way -- all is futility! Then the Lord told me to turn to the book of Job. In Chapter 23:10 "But if I go to the east, He is not there; if I go to the west, I do not find Him. When He is at work in the north, I do not see Him; when He turns to the south, I catch no glimpse of Him. But He knows the way that I take; when He has tested me, I will come forth as gold." In Chapter 42:5, Job says, "My ears had heard of You but now my eyes have seen You. Therefore I despise myself and repent in dust and ashes."
Results:
1. I realized I was not the first to feel this way. (Ecclesiastes)
2. I realized that even if I could not see God's hand at work in my life: He was there and He had a purpose. (Job 23:10)
3. I realized my arrogance for wanting to take my God-given life & I got down on my knees before my Creator and asked forgiveness for not giving Him the respect He deserves, for my self-centeredness and my wrong desire to control my own life. (Job 42:5)
4. I received a new start in my life & I now experience what it means to realize that "Through the Lord's mercies we are not consumed, Because His compassions fail not. They are new every morning; Great is Your faithfulness. ' The Lord is my portion,' says my soul, Therefore I hope in Him!" Lam. 3:22-24
Suicide is probably the most distressing thing that can happen to a family and it leaves people bewildered & wondering what happened to the soul of the one who died. We cannot judge if the deceased had a relationship with the Lord, but we can determine that the relationship was not on the best of terms or the suicide would never have taken place. We all succumb to sin at one time or another. We need to be compassionate at such a time, not judgmental. There is NO WAY to tell if the person was truly born again; we must leave that in the capable hands of the Lord. But one thing is sure - the Sin Issue is forever settled in the eyes of the Righteous Judge. Y'shua (Jesus) paid it all on the tree! No one will be judged for sins -- not here, not ever. The Blood of Y'shua atoned for the sins of the world. (I Jn 2:2)
The Final Judgment will be based on works - things which unbelievers think are good enough to get them to heaven. At the Final Judgment, the Lord will give them an opportunity to compare their "good deeds" with His own Righteousness. (books of works - Rev. 20:11-15) Then they will realize their works are nothing but "filthy rags in His sight." (Isaiah 64:6) They will come up miserably short compared to the glory & purity of the Most High God. The ONLY WAY to get right with God is to accept His Messiah as a blood atonement for our sins. That is God's provision. Once in the family of God, He is well able to take care of His children & He is well able to spank those who misbehave. Trust in Him.