How do we know that all have sinned in Adam?

Scripture states that through one man's disobedience, many were constituted sinners (Romans 5:19). This implies that when Adam sinned, he represented all of humanity. As such, his transgression brought about spiritual death, and all mankind shares in this fallen nature. It is important to understand that this does not merely mean that we bear the guilt of Adam's sin, but rather, we participated in his sin as our federal head. Adam's sin made each individual a sinner by nature, thus necessitating the grace found in Christ for redemption.