Spiritual Death
Spiritual death is humanity's separation and alienation from God because of sin. It describes a person's condition outside spiritual fellowship and life with God, not the inability to hear, understand, or respond to God's call.
Expanded explanation
Spiritual death describes the human condition apart from fellowship with God. Sin alienates people from their Creator, leaves them under the power and consequences of sin, and places them in need of the life and reconciliation God provides through Christ.
That condition should not be confused with the claim that people are unconscious, unable to understand, or unable to respond to God's call. A person can be spiritually separated from God while still hearing the gospel and being responsible to receive it. Spiritual death means that people need God to save them; it does not mean that they must first be regenerated before they can believe.
Jesus' description of the prodigal son provides a helpful picture. The son was described as dead and then alive, yet he came to his senses and returned to his father. The illustration does not answer every theological question, but it shows that relational death does not require the absence of awareness or the inability to return.
God alone gives spiritual life and accomplishes salvation. The question is not whether people can create life in themselves. They cannot. The question is whether a person who is separated from God can respond when God graciously calls through the gospel.
Context
The language of death can describe separation, alienation, and the loss of relationship as well as physical cessation. The prodigal son was described as dead and then alive, yet he came to his senses and returned to his father. That parable is not a complete technical explanation of the order of salvation, but it illustrates how death and life can describe a broken relationship and its restoration.
Passages about spiritual death should therefore be read alongside their calls to repent, believe, return, and be reconciled. The texts affirm the seriousness of sin and the necessity of God's grace without requiring that dead people be unable to respond to the gospel.