What was Jesus's mission?

The mission of Jesus Christ was to come into the world and to die for our sins on the cross at Calvary.

Additional Answer:

"The time is fulfilled, and the Kingdom of God is at hand. Repent, and believe in the Gospel." Mark 1:15

Christ did NOT come to destroy the Law (Law of Moses) rather He came to fulfill it or 'fill to the rim' the Law. He corrected the wrong and burdensome teachings of the Pharisees/Sadduces/Scribes and explained the spiritual aspects of the Law like just looking at a woman in a lustful way breaks the Commandment on Adultery.

Because Christ would become our Passover sacrifice, the old Sacrificial Laws were absolved. He became our Eternal High Priest so the Levitical Priesthood was discontinued. Due to these necessary changes for a perpetual New Covenant, other smaller amendments took place. BUT no way was any of the Commandments discontinued or modified. Indeed, Christ added to the old commandment to 'love your neighbor as yourself' but commanding now to 'love your neighbor as I have loved you. We all know that no greater love is there than to give your life for your fellow man.