Crucifixion was a powerful symbol throughout the Roman world. It was not just a means of liquidating undesirables; it did so with the maximum degradation and humiliation. It said, loud and clear: we are in charge here; your are our property; we can do what we like with you. It insisted, coldly and brutally, on the absolute sovereignty of Rome, and of Caesar. It told an implicit story, of the uselessness of rebel recalcitrance and the ruthlessness of imperial power. It said in particular: this is what happens to rebel leaders. Crucifixion was a symbolic act with a clear and frightening meaning. [Wright, Jesus and the Victory of God, pg. 543]
Given this apt description and its symbolic value in the socio-historical context, Jesus must have been summoning disciples to a counter imperial allegiance. An allegiance to the Empire of YHWH. Jesus was appealing for a conversion of allegiance from the Roman Empire and everything else, to himself. In affect, it appears as if Jesus was asking them to become apostates of their faith and to rather embrace him as their true King.
But this begs the more important question of why Jesus would use such an image? This piece of the data must fit into our overall hypothesis, which I think many in the "Third Quest" have yet to do. Following Wright (JVG) and Trocmé (Jesus and the Non-Violent Revolution) Jesus was posing a revolution [although that's a slippery word) but not the sort Reimarus had in mind. Jesus' revolution was one of non-violence, of going the road of passive resistance. According to Trocmé's analysis, his portrait is of a vigorous revolutionary capable of saving the world without using violence. It was a road of defeating the love of power [Rome and the Satan] with the power of love. It was a road marked by non-compromise to the gods of this world. Augustus had set himself up as LORD and SAVIOUR but Jesus was challenging that very understanding. Emperors like Tiberius and those that would follow, were not the true LORD and SAVIOUR. They were tyrants who wanted to use Power to control the populace. But to follow Jesus in accepting him as their true Kyrios, meant that they would follow a path that would almost certainly lead to their death, as it finally did with Jesus.
To follow Jesus is to accept a path that will lead to pain and suffering and probably death. As Keener says, the demands of the kingdom are so offensive to a world alredy convinced of its rightness that they provoke tht world's hostility. [Keener, Matthew, pg. 329]. Keener goes on to suggest that the whole context of Jesus' ministry, and language may even indicate that Jesus' mission would inaugurate the messainic woes, the ultimate tribulation for his followers.
So in our tradition about picking up one's cross, and embracing Jesus as Master, the convert is being called to embrace a vocation that is implicitly counter-imperial - it is bearing a cross. The way of the cross is the way of revolting against Rome and her oppresive idealogy and praxis. It is the way of submitting to another King, named Jesus.