Adam was the first human created by God's image and likeness. Adam was given dominion over the earth, so therefore this made him the head over mankind. When Adam sinned, it was passed on from generation to generation, it was inhertited. In this light we were borned with a sinful nature. God's plan of redemption was for Christ, who is referred to as the Second Adam in (1Corithians 15:45,46) to redeem the sinful man back to Him, through the shedding of innocent blood (His Son). Through Christ we have access to God's grace. Christ became the head of the New Body of redeemed believers, first through Faith (Belief), God's grace (Favor) and then being made righteous. Christ died on the cross so that we (Mankind) may live, He gave us victory over death (which is sin).