The first representative man was Adam. By the creative power of God, He came forth from the dust of the ground and stood before His Maker as the appointed representative of all mankind. This position is sometimes referred to as his federal headship. When our federal head sinned against the Lord, he led all of his posterity into rebellion with him. We all had a part in his transgression and, consequently, we all share the effects of it, as well as the guilt of it. "Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned" (Romans 5:12). All of those Adam stood for, all of humanity, are contaminated with sin by reason of our representative's transgression. We are legally declared to be guilty before God of sinfulness. "For by one man 's (Adam's) sin, many (all he represented) became (were legally rendered or constituted to be) sinners" (Romans 5:19a). Friend, do you see that we became unrighteous through the unholy action of somebody else? We do not sin in order to become sinners, we were born sinners, therefore, we commit sin. "Behold, I was shapen in iniquity; and in sin did my mother conceive me" (Psalm 51:5). The man who stood as our representative with God made a deadly choice and plunged us all into a state of guilt, spiritual death and sin.
Thank God, however, there is another Representative, the Son of God. He, like Adam, was a representative Man, and was so from before the foundation of the world. In fact, the Lord Jesus Christ is called "the last Adam" (1 Corinthians 15:45). In the covenant of grace, Christ was appointed to be the Representative of all those chosen by the Father unto salvation. "By so much was Jesus made a Surety of a better testament" (Hebrews 7:22). As God looked at Adam's transgression and dealt accordingly with all mankind, declaring them to be sinful, so God looked at Christ's obedience and dealt accordingly with all those He represented, proclaiming them to be righteous. "By the obedience of One shall many (all Christ represented, the elect) be made (legally constituted to be) righteous" (Romans 5:19b). "As in Adam all die, so also in Christ shall all be made alive" (1 Corinthians 15:22). Adam is the cause of death, but Christ is the cause of life. Even as all of Adam's seed were rendered sinful and legally constituted to be spiritually dead in him, so all of Christ's seed were rendered righteous and legally constituted to be spiritually and eternally alive in Him before God.