According to the Holy Bible, spiritual death refers to the soul’s separation from God. Thus, unlike physical death, which is a separation of body and soul, spiritual death refers to separation of man and God.
It happens due to sins and our own disobedience to His gospel. For instance, when Adam sinned against God by eating the forbidden fruit, he died spiritually but continued to live physically fro numerous years.
Thus, it is believed that we are all born spiritually dead, or in other words, spiritually separated from God.
However, through the Atonement of Jesus Christ, one can be redeemed from spiritual death, having faith in Jesus Christ.
On the other hand, spiritual death can also be interpreted as death in a spiritual way. Simply put, it means, dying while identifying oneself as a spiritual being, not as a mere physical body.
When identifying ourselves with the material world, we ignore our eternal spiritual nature, which is the essence of life.
However, dead matter cannot influence the changeless Spirit. You can find out more about this concept of spiritual death at Wikipedia.
Spiritual Death Quotes
And the LORD God commanded the man, “You are free to eat from any tree in the garden; but you must not eat from the tree of the knowledge of good and evil, for when you eat of it you will surely die”
And if Christ is in you, though the body is dead because of sin, yet the spirit is alive because of righteousness.
For if you live according to the sinful nature, you will die; but if by the Spirit you put to death the misdeeds of the body, you will live.
For the gospel has for this purpose been preached even to those who are dead, that though they are judged in the flesh as men, they may live in the spirit according to the will of God.
1 Peter 4:6
But your iniquities have separated
you from your God;
your sins have hidden his face from you,
so that he will not hear.
But Jesus said to him, “Follow Me; and allow the dead to bury their own dead.”
By no means! How can we who died to sin still live in it?
So you also must consider yourselves dead to sin and alive to God in Christ Jesus.
I tell you the truth, if anyone keeps my word, he will never see death.
When you were dead in your sins and in the uncircumcision of your flesh, God made you alive with Christ. He forgave us all our sins, having canceled the charge of our legal indebtedness, which stood against us and condemned us; he has taken it away, nailing it to the cross. And having disarmed the powers and authorities, he made a public spectacle of them, triumphing over them by the cross.
Very truly, I tell you, anyone who hears My word and believes Him who sent Me has eternal life, and does not come under judgment, but has passed from death to life.