While they were all amazed at his every deed, he said to his disciples,
"Pay attention to what I am telling you. The Son of Man is to be handed over to men."
But they did not understand this saying; its meaning was hidden from them so that they should not understand it, and they were afraid to ask him about this saying.

Gospel commentary

Saint Thomas Aquinas (1225-1274), Dominican theologian, Doctor of the Church
Commentary on the Letter to the Galatians, ch. 6

Some people draw glory from their knowledge, but the apostle Paul finds supreme knowledge in the cross. “No, he says, I desired to know nothing among you but Jesus Christ and Jesus Christ crucified” (1 Cor 2:2). Is not the cross the fulfilment of the whole law and art of living well? To those who glory in their own power, Paul can answer that he draws matchless power from the cross: “The language of the cross is foolishness to those who are perishing, but to us who are being saved it is the power of God” (1 Cor 1:18). Do you draw glory from the freedom you have gained? Paul draws his from the cross: “Our old self was crucified with him (…) that we might no longer be slaves to sin” (Rm 6:6).

Yet others draw their glory from being chosen as members of some famous group or other ; but as for us, through Christ's cross we are invited to the congregation of heaven. “Reconciling all things, whether those on earth or those in heaven, making peace by the blood of his cross” (Col 1:20). And finally, some people glory in the insignia of victory bestowed on the victorious, but the cross is the triumphal standard of Christ's victory over demons: “He destroyed Principalities and Powers, making a public spectacle of them, leading them away in his triumphal procession” (Col 2:15) (…)

What is it that the apostle Paul wants to glory in above all else ? In that which can unite him to Christ. For what he desires is to be with Christ.