1. The Agony in the Garden
Jesus, taking a few of the Apostles with Him, went into the garden and prayed until He sweat, until He was clearly in anguish. Jesus boldly prayed to be spared His Passion, but submitted His will to that of the Father's. This mystery, along with the crowning with thorns and carrying of the cross, reflect the necessity of sacrifice, of service unto pain and death--suffering brought upon a king by his needful subjects, in their need for more than administration and leadership--for those who look to Christ as savior and king, and for those who look to us as Christians to guide and be an example to.
2. The Scourging at the Pillar
Our sins consign to us guilt and punishment, both temporal and eternal. While Pilate had Jesus whipped to satisfy the baser appetites of the mob rather than out of a properly motivated sense of justice, it shows us that we should not expect a free ride through life, and that justice is not extinguished by love and mercy, even though our salvation was brought to us gratuitously. Christ calls us all to mortifications of a sort, and asks us all to be like Simon of Cyrene in some way.
3. The Crowning with Thorns
In one of the cruelest parodies of His ministry, the Romans mocked Him and placed a crown of thorns upon his head. God is strongest in the weak, however, and confounds the proud by raising up the meek. The Romans acknowledge in a backhanded way Christ's kingship of the humble, the downtrodden, the ones who will be subjects in the only kingdom that matters. The king of the weak, and the king of the Jews, is also the king of kings.
4. The Carrying of the Cross
Christ carried His burden--our burdens, our sins, us--to Golgotha, because only He could. Simon's reluctant aid doubly reflects Christ sharing with us His Passion, as He will share His union with the Father with us in heaven, and the stilling of our own concupiscence.
5. The Crucifixion and Death of Jesus
Christ was rejected by the world but still saved it. He was the sacrifice, and through the instrumentality of the Romans, also the priest. We cannot save ourselves, and will only crucify God (which, without His resurrection, will leave only us as the dead ones) when left to our own devices, but God deigns to work through us, out of love and as a sign of the good we're supposed to do for each other.