According to philosopher and advocate of libertarian free will, Robert Kane, autonomy is having the “power to be the ultimate creator and sustainer of one’s own ends or purposes” (The Oxford Handbook of Free Will. Second Ed. 382-383). And, as Kane suggests, if a human being has the essential property of autonomy, then no other being can have ultimate authority in one and the same choice when the human agent is using her power to be the ultimate creator and sustainer of her own ends and purposes.
It seems to me that choosing an external authority, such as a deity, is a case of a human agent using his or her autonomous choice. However, the kind of authority that it is possible to choose is limited to those which meet the autonomous criteria already chosen by the person. For example, if one is to choose a dentist to treat a painful incisor a criteria by which the dentist is chosen is determined on the basis of a criteria that originates within the parameters set by the autonomous human agent. Jesus Christ could be accepted on such terms as an authority. He conforms to the preferences found in the autonomous self for good behavior (one might trust him in this sense) and for expertise in spiritual matters (he appears to have some access to the divine, perhaps he is even himself divine).
If one accepts Kane’s claim an authority can only be accepted on terms within the agent. This might be reason, evidence, moral, or even a denial of all those (a leap of faith), but those criteria are chosen on the basis of an ultimacy found solely within the human agent. An authority that cannot, I think, be accepted is an authority whose means of attestation is found only within the authority itself.
Consider when one chooses to believe in God, a self-attesting ultimate authority. If one chooses to believe in God one cannot, if we follow Kane’s logic, choose it solely on God’s own authority because the criteria by which one chooses to believe God has already been decided by the autonomous agent. The problem with this is that God claims to be the the only basis for choosing to believe in God – he is his own authority on God. There is no test outside God by which one might measure God’s claims to be God.
It is a stark choice: either God is not ultimate, or cannot be self-attesting, or there is no such thing as “a [human] power to be the ultimate creator and sustainer of one’s own ends or purposes.”
One might wonder if there is any way to choose to place oneself “under” the authority of Christ. Some might be satisfied to remain committed to the idea that human agents have the ultimate autonomy in question. Their sense of authority is, in my view, a little weaker than I think the Bible describes Christ’s absolute claim to Lordship. Lordship is total, absolute; it is a claim to be the only authority, to be the only ultimate.