Confession clarifies Confusion

Christ, in the work of mediation, acts according to both natures, by each nature doing that which is proper to itself; 

yet, by reason of the unity of the person, that which is proper to one nature is sometimes in Scripture attributed to the person denominated by the other nature.  

[Westminster Confession of Faith 8.7]

The works that Christ did, then, were not simply the works of a human; they are the works of the mediator, who is both fully God and fully man. Therefore the value of Christ's death is infinite because of the worth of the person. In other words, one who was a human being only could not have paid the debt owed to God for so great a number of people. Yet because Christ had a true human nature he was able to pay the debt on behalf of sinful humanity. [p22-23 of Mark Jones' A Christian's Pocket Guide to Jesus Christ.]