WELS affirms that all humanity, except Jesus Christ, is born in sin and guilt as a consequence of Adam's transgression. Original sin is not merely a propensity toward sin or a bad habit inherited from Adam's example; rather, Adam's sin is imputed to all his descendants, and all are born with inherited guilt and spiritual corruption.

Total depravity is affirmed: before conversion, the human will is enslaved to sin and cannot, of its own power, turn to God, believe the gospel, or perform any work pleasing to God. The will is not weakened by sin but is entirely incapable of spiritual good apart from the regenerating work of the Holy Spirit. This corruption extends to the entire person—intellect, will, emotions, and body.

Infants are born in original sin and guilt, though the LCMS holds that they stand under the universal atonement and can be regenerated through baptism. WELS does not teach that unbaptized infants who die are automatically damned, but this matter is entrusted to God's mercy and justice. Original sin is the theological foundation for understanding the necessity of Christ's atonement and the work of the Holy Spirit.