In Matthew 16:24 Jesus tells the Apostles to take up their cross and follow Him. How does this make sense to them? Surely crucifixion was already practiced, but how would they have understood this coming from Christ, who had yet to be crucified and not established the significance of “taking up the cross”?
They may have understood the statement incompletely, but they couldn’t have missed the point entirely.
Looking at this verse in context makes it a bit clearer:
(The translation I’m quoting here is the “Catholic Public Domain Version”)
*Mat 16.21 From that time, Jesus began to reveal to his disciples that it was necessary for him to go to Jerusalem, and to suffer much from the elders and the scribes and the leaders of the priests, and to be killed, and to rise again on the third day.
Mat 16:22 And Peter, taking him aside, began to rebuke him, saying, “Lord, may it be far from you; this shall not happen to you.”
Mat 16:23 And turning away, Jesus said to Peter: “Get behind me, Satan; you are an obstacle to me. For you are not behaving according to what is of God, but according to what is of men.”
Mat 16:24 Then Jesus said to his disciples: "If anyone is willing to come after me, let him deny himself, and take up his cross, and follow me.
Mat 16:25 For whoever would save his life, will lose it. But whoever will have lost his life for my sake, shall find it.
*
So, this passage - which comes right after St. Peter’s declaration of faith - is Our Lord’s explicit prophecy that he is to suffer, die and rise from the dead. The statement about “taking up one’s cross” is followed by a reiteration of the same theme. The disciples cannot truly follow Him without being ready to dedicate their earthly lives to Him, even to the point of martyrdom - which is what eventually happened to St. Peter,
inter alia.
While the meaning of the “cross” might have remained unclear to them until His Passion, I think they would certainly have understood Him in a general sense.