It's useful to compare and contrast the mission of Christ from an orthodox standpoint with the mission of Christ from a unitarian standpoint. Heresy can unwittingly illuminate truth. We're so used to the right reading that contrasting that with a wrong reading can help us to appreciate things we might not otherwise notice.
Reading the mission of Christ through an orthodox (e.g. Reformed, Incarnational, Trinitarian) lens, it goes basically like this:
The Father sends the Son on a redemptive mission. This was a timeless, Trinitarian plan of salvation, in which each member had a role to play. The Son not only knows the details of the plan, he had a hand in formulating the plan. He knows in advance exactly what to expect. He agreed to that.
That's a somewhat anthropomorphic way of putting it. To be more precise, the plan existed from all eternity.
Moreover, his atonement is inherently supererogatory. For the Creator to submit to creatures, for the sinless Son to die for sinners, is intrinsically above and beyond the call of duty.
Now let's read the mission of Christ through a unitarian lens:
Jesus is a fallible shortsighted human being. As a zealous, idealistic Jew, he has a sense that God is calling him to go on a mission. But Jesus doesn't know what he's getting into. Because he imagines that God has his back, Jesus takes crazy risks. And because he eludes the lynch mob on more than one occasion, that emboldens him. But just when events come to a head, God deserts him. God withdraws the backup.
Or maybe Jesus was deluded all along. He keeps sticking his neck out because he figures God will protect his servant. But that's wishful thinking. In the end, he was hung out to dry. At best, just another Jewish martyr. At worst, God's fall guy.
The unitarian Jesus is a dumb schmuck who walked right into a trap that God could see coming from miles away. The unitarian Jesus didn't know what hit him until it was too late. And his death is so pointless anyway.
Unitarian theology implicitly casts God in a sinister light. In unitarianism, God is to Jesus as David is to Uriah. Or, to take an illustration from John LeCarre (Tinker, Tailor, Soldier, Spy), God is to Jesus as Bill Haydon is to Jim Prideaux. Haydon is a high-ranking spy in MI-5. Control and George Smiley are attempting to ferret out the spy in their midst. Haydon needs to do something to throw them off the scent.
So he sends his old friend and subordinate, Prideaux, on a mission. Prideaux believes he will meet with a Czech general who intends to defect. But it's a setup. Haydon tips off the Czech authorities. Prideaux is shot in the back and tortured. When returned, he's a broken man.
But the plan succeeds in the sense that it terminates the investigation. Control and Smiley are sacked. Haydon is promoted.
There were two different missions: the mission Prideaux thought he was going on, and the actual mission that Haydon had in mind, that Haydon kept to himself.