I have been a Christian for many years. I went to Sunday schools and Bible studies numerous times and have discussed God's self existence a few times. However, I could not find any passage in the Bible saying that God is self existent.

The following passages are often used as the evidence for God's self-existence.

1. Exodus 3:14. I AM THAT I AM.
2. Colossians 1:17. And he is before all things, and by him all things consist.
3. Revelation 1:8. I am Alpha and Omega, the beginning and the ending, saith the Lord, which is, and which was, and which is to come, the Almighty.
4. Revelation 22:13. I am Alpha and Omega, the beginning and the end, the first and the last.

According to Wikipedia, the original Hebrew for "I AM THAT I AM" can be literally translated as "I-shall-be that I-shall-be." Therefore, this passage is actually related to God's eternity. It tells nothing about God's self-existence.

The second passage clearly says that God existed "before all things". However, in the second half, it also says "by him all things consist". Therefore, the "all things" means everything in our world. This passage is related to the creation of our world by God. Of course, a creator must have existed before the created things. The passage did not say how the creator came to exist.

The last two passages seem to provide a strong evidence for God's self-existence because they explicitly state that God is "the beginning". However, "the beginning" here means the beginning of our world. It does not mean the beginning of the Kingdom of God. The third passage says "the beginning and the ending". The Kingdom of God is eternal. It has no ending. Again, the two passages are related to the creation of our world and God's eternity, not to God's origin.

The entire Bible wants us to know that our world was created by God, who is eternal. However, the Bible did not tell us anything about the origin of God. In previous articles, we have shown that our world could be created by the highly intelligent life living in the higher dimensional space (the bulk universe). Scientifically, this intelligent life can be immortal (just think of the stem cell technology which will dramatically increase our lifespan), but cannot suddenly appear out of nowhere. From the scientific point of view, the complex life must evolve from simple structures. In fact, the physical laws allow the complex life to evolve from the vacuum (see The String Theory and the Origin of God).