Two others also, who were criminals, were led away to be put to death with him. When they came to the place that is called The Skull, they crucified Jesus there with the criminals, one on his right and one on his left. Then Jesus said, "Father, forgive them; for they do not know what they are doing." Luke 23:32-34
I desire mercy not sacrifice, God says to the prophet Hosea. The final words of Christ begin with mercy. Yet it is an odd kind of mercy. 'They do not know what they are doing', he says. The people who crucify Jesus are surely conscious of their actions. In what way do they not know what they do?
Broadly speaking, Christ's first word on the cross is a description of us all when we sin. All of our sins, all of our actions against the peace of God, against the Shalom of God, all of the ways we hurt our neighbors and ourselves we do without really knowing what we do. We may, from time to time, deceive and realize that we are deceiving, but the magnitude of our action is never apparent.
In our sin, we put Christ on the cross because Christ takes away our slavery to deception. Christ's freedom means we don't have to just think of our selves and our own pleasure, yet sometimes we want to. Sometimes we are tired of being good and we just desire our own self fulfillment.
God is not angry with us for God only ever loves us. God wishes to take away our lust for power. To take away our pride. That is the mercy of Christ on the cross.
Christ's first word is to us. Even though we don't know what we do, Christ still shows us mercy. Even when we think we know what we do, Christ still shows us mercy. When we deserve curses and damnation, we are given mercy.