In Luke 2.34, the baby Jesus is presented in the Temple. There, the prophet Simeon speaks about the future of the child. Simeon calls Jesus a "sign of contradiction": "And Simeon blessed them, and said to Mary his mother: Behold this child is set for the fall, and for the resurrection of many in Israel, and for a sign which shall be contradicted ..."
This is from the Douay–Rheims translation. Most translations have "a sign that will be opposed" or "a sign that will be spoken against". The word "sign" here is the Greek word σημεῖον (sémeion). Sémeion occurs 77 times in the NT and it has a few different meanings. But its basic meaning is that which makes something distinctive, salient, noteworthy or different. This could be a token or a mark that sets a person apart from others. Circumcision, for example, is called a "sign" (Romans 4.11). Signs can also be portentous events. Signs are those events that suggest that something is coming down road, the first rumblings of thunder, for good or ill. Thus we speak of "signs of the times", like in Matthew 16.1-3.
Because sémeion refers to events or things of a distinctive or noteworthy nature, sémeion is also the word that gets translated as "miracle" or "miraculous sign" in the gospels.
But I want to point out something important today: Miracle isn't a biblical word. The gospel writers use other words like sémeion and we, the English reader, describe these signs as "miracles". But that shifts the frame a bit. The word "miracle" shifts the focus to causality. To be sure, Jesus is described as doing things that defy the normal laws of cause and effect. But the "miracles" are, fundamentally, signs. The actions of Jesus are portents. The signs are pointing and gesturing toward something.
That leaves open a question: A sign of what?
A sign, according to Simeon, that would be opposed, resisted and spoken against. A sign of contradiction.
In Mark 8 the religious authorities ask for a miraculous sémeion, a "sign from heaven". Jesus says they won't get one. Not, at any rate, the sort of sign they were hoping for. Because there is a sign standing right in front of them. They just can't see it, see him. Instead, they will contradict, fulfilling the oracle of Simeon. As Jesus goes on to describe in Mark 8: "He then began to teach them that the Son of Man must suffer many things and be rejected by the elders, the chief priests and the teachers of the law, and that he must be killed ..."
But there's more. Jesus continues: "Then he called the crowd to him along with his disciples and said: 'Whoever wants to be my disciple must deny themselves and take up their cross and follow me'".
Just as Simeon foretold the future of Jesus, Jesus foretells the futures of those who follow him.
I'm always struck by how stark this language is. We attempt to spiritualize it, but I think -- along with Bonhoeffer in his Cost of Discipleship -- that there's so much we miss, so much we "cheapen" in that way.
Like Jesus, we are to become signs of contradiction. We are to become tokens, portents and omens that speak, enact and dramatize the contradiction with this "present evil age". We are to become signs of contradiction -- miracles, even -- of God's reconciling love in the world.