In its upper right hand corner, the shield contains a “crown with thorns.” This emblem, with a kingly crown resting atop the thorns reminds us that Jesus was a suffering Christ; this of course, was scandalous to the Jews of Jesus’ time and to many today. But the Messiah, the anointed one of God, was anointed, not to rule on the earth presently, but to suffer and die for our sins.
Christ’s kingdom, though real, is a spiritual kingdom, not an earthly one.  This emblem, then, serves to remind us of the great paradoxes of the faith, as well as constituting a subtle reminder that the Church of Jesus Christ is to be in the world, but not of it, and that the true church should expect always to be marked by persecution as we complete the suffering of our Lord, as St. Paul put it.  It’s not always going to be smooth sailing, but that said, Christ is King, and one day he will return as such and we shall reign in a consummated kingdom with him, in a new earth under new heavens!