I have been mulling this over for a few days and came to this. My two cents worth, hopefully it will add to the discussion.
Isa_59:2 But your iniquities have separated you from your God; And your sins have hidden His face from you, So that He will not hear.
Spiritual dead = separation from God
Spiritual life = in Christ
Sin separates one from God
Adam sinned = separated from God
Adam spiritually dead
Spiritual death, which is the death of the soul and spirit of man (Ephesians 2:1), where the apostle mentions being “dead in trespasses and sins”). This results from the separation of the soul from God, by the breaking of the silver cord of this covenant, which knit innocent man to God, causing him to live, and live prosperously, as long as it was unbroken; but being broken, that union and communion was dissolved, and they parted (Isaiah 59:2). Thus man was separated from the fountain of life, upon which death necessarily ensued. The Biblical Illustrator - Joseph S. Exell Genesis 2:16-17
Died Spiritually
Paul wrote about being spiritually dead.
Once I was alive apart from law; but when the commandment came, sin sprang to life and I died (Romans 7:9).
Did Paul physically die? No. But there was separation between him and God through sin.
Spiritually Dead
The Prodigal Son provides a good illustration of one who is said to have been dead/separated from the father.
But we had to celebrate and be glad, because this brother of yours was dead and is alive again; he was lost and is found (Luke 15:32).
Result Of Sin
The reason we are all born spiritually dead has to do with sin. We receive our fallen nature from our parents. The warning was given. (Genesis 2:17) After Adam and Eve sinned they hid from God, (Genesis 3:8-10) the death sentence was pronounced. (Genesis 3:19) All other humans have been born with their sinful nature (the exception to this was Christ Jesus who was born without sin). Therefore each of us comes into the world spiritually separated from God.
My Conclusion
All of us are born spiritually dead, or separated from God. This is because all of us have inherited the sin nature from Adam and Eve.