I agree with you that before we were born we all were non-existent and that is as far as I go with you in agreement.
There are some who would disagree with us because they believe in re-incarnation.
To continue on, naturally of course, I disagree with you that we return to being non-existent again like how were before we were born when we die our physical natural deaths.
Once you begin to exist in a human body your soul becomes eternal.
Let me give you a passage in the bible, "The Scriptures tell us, the first man, Adam, became a living person. But the last Adam---that is, Christ---is a life giving Spirit. What comes first is the natural body, then the spiritual body comes later. Adam, the first man, was made from dust of the earth, while Christ, the second man, came from heaven. Earthly people are like the earthly man, and heavenly people are like the heavenly man. Just as we are now like the earthly man, we will someday be like the heavenly man. What I am saying, dear brothers and sisters, is that our physical bodies cannot inherit the Kingdom of God. These dying bodies cannot inherit what will last forever" (1 Corinthians 15:45-50)
Therefore, it is clear that we have no pre-existence before we were born and we will have a spiritual existence after we die our natural deaths.
One verse that is commonly used is Jeremiah 1:5, "I knew you before I formed you in your mother's womb." But this verse is not talking about pre-existence. It is talking about God’s ordination and appointment of Jeremiah to be a prophet to his nation. Let’s look at the whole verse: "I knew you before I formed you in your mother's womb. Before you were born I set you apart and appointed you as my prophet to the nations."
One more point worth looking at is how God uses the word "know." For example, the Bible says that God only knows believers, not unbelievers. "My sheep listen to my voice; I know them, and they follow me" (John 10:27);
and ".....The Lord knows those who are his," (2 Timothy 2:19); and,
"Not everyone who calls out to me, "Lord! Lord! will enter the Kingdom of Heaven. Only those who actually do the will of my Father in heaven will enter. On judgment day many will say to me, "Lord! Lord! We prophesized in your name and cast out demons in your name and performed many miracles in your name. But I will reply, I never knew you. Get away from me, you who break God's laws." ---Matthew 7:21-23
Of course, God knows who everyone is, He is omniscient. But God is showing us that when He says He knows us, He is referring to a salvation relationship.
Therefore, we did not preexist. We are born here in this world and will enter the next.
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