Chalcedon had confessed two natures in one person. A further question followed: if Christ has a divine nature and a human nature, does he have one will or two? Monothelitism — from the Greek for 'one will' — held that Christ had a single will. It was offered, in part, as a bridge to the non-Chalcedonian churches.
Two Wills
The council, drawing on the work of Maximus the Confessor, answered that Christ has two wills, divine and human, because a complete human nature includes a human will. To deny Christ a human will would be to leave his humanity incomplete — and what is not assumed is not healed. The two wills are not in conflict: the human will of Christ moves in free, full, and perfect accord with the divine.
Gethsemane
The council's confession gives weight to the garden of Gethsemane. 'Not my will, but yours, be done' is not a divine person overruling himself; it is the human will of the incarnate Son, genuinely human, freely and fully surrendering to the will of the Father. The salvation of human willing runs through that prayer.