The work which Jesus came into this world to accomplish was the reconciliation of sinful man to God.  Through the original sin of Adam and through the personal sins which men of all times have committed, man had alienated himself from God, and had incurred an infinite debt by his sin, a debt which he was absolutely helpless to repay.  By his disobedience Adam forfeited for himself and for all his descendants the divine life of grace, which God had given him as a free, undeserved gift.  This gift, grace, had set a supernatural goal or purpose for man's life.  Original sin had lost this life of grace for man, and rendered him absolutely incapable of reclaiming it.

Now, God could have overlooked man's sin, ignored his fall, and completely reinstated man in His love and friendship.  But it is difficult to see how such action could be reconciled with God's infinite justice, which would certainly seem to require some reparation for man's voluntary rebellion.  On the other hand God could have condemned the whole race to the penalty of forfeiting the eternal joy of heaven for which He had created man, and even of undergoing the eternal torments of hell, even for a single mortal sin.  But it is difficult to conceive how such a plan would leave room for the divine mercy, even though it would completely satisfy divine justice.

The infinite wisdom of God gave the perfect answer to this dilemma.  God wanted atonement for man's sin, equal to the offense.  Man's offense against God is infinite, for the gravity of all offenses or insults is measured by the dignity of the one offended, in this case God.  Man, being finite or limited, could offer no proportionate reparation.  Therefore, God Himself became man to suffer and die for sinners.  The value of His action, His suffering and death, is infinite (for the value of meritorious actions is measured by the dignity of the one performing them).  Christ alone, therefore, could and did offer complete and adequate payment for man's debt before God. 

Yet this Godman, Jesus, is truly human and so acted as man's representative or mediator before God.  He alone effected man's reconciliation with God by becoming "obedient to death, even to death on a cross" (Phil. 2:8).

This is the essential work for which God became man.  And His work is continued and applied to men through the Church which He founded.  To add to the effectiveness of His work, Christ also taught men religious truths and manifested in His own life the perfect example of human living.

Encyclopedia Dictionary of the Bible