When James and John, the sons of Zebedee, approach Jesus and ask him that they be seated at his right and left in his kingdom, his response is to question them: Are you able to drink the cup that I drink, and be baptized with the baptism that I am baptized with? (Mark 10.38). They respond, of course, that they can. So he tells them: The cup that I drink you will drink; and the baptism with which I am baptized, you will be baptized (v. 39).
Jesus is speaking about his sufferings, the 'cup' and 'baptism' of his crucifixion and sufferings. What he tells James and John, who were so eager to occupy positions of glory in Christ's kingdom, is that they are going to pass through sufferings and trials of this sort as well. They have their eyes on a seat of power and influence and glory, but Jesus warns them that what is coming is grave suffering and misery. As he said to the disciples on an earlier occasion, "Children, how hard it is to enter the kingdom of God!" (v. 24); those who enter the kingdom receive houses, brothers and sisters, mothers and children, and fields, with persecutions (v. 30).
Perhaps one of the most important metaphors for the process of Christian salvation is union with and participation in Christ; we are united with Christ and begin to participate in his recapitulation of human life. For instance, in baptism we are united to him in his death to sin and resurrection to life to God (Rom 6.5-11). But this union with Christ comes with good stuff and bad stuff, too, if I may put it that way. Union with Christ means union with the suffering Christ, who told us that entry into the kingdom of God is a difficult matter indeed: For mortals it is impossible, but not for God; for God all things are possible (Mark 10.27).
Paul tells us in the letter to the Romans: When we cry, "Abba! Father!" it is that very Spirit bearing witness without our spirit that we are children of God, and if children, then heirs, heirs of God and joint heirs with Christ -- if, in fact, we suffer with him s that we may also be glorified with him (Rom 8.15-7). Just as Christ first suffered and then inherited glory, so also Christians must first suffer in order to be welcomed into glory on the other side. Likewise Peter says to rejoice insofar as you are sharing Christ's suffering, so that you may also be glad and shout for joy when his glory is revealed. If you are reviled for the name of Christ, you are blessed, because the spirit of glory, which is the Spirit of God, is resting on you (1 Pet 4.13-4).
If union with Christ and participation in Christ means suffering with Christ, then we should not be surprised when it happens to us. Of course, not all suffering is suffering with Christ; sometimes we suffer because we have done wrong (cf. 1 Pet 4.15), other times because we are stupid, and so suffer deservedly. But we should not have the illusion that the Christian life does not involve any suffering whatsoever, or that a Christian might not suffer even gravely, deeply, feeling as Christ did on the cross that God has abandoned him. The answer is to trust God in suffering just as Christ did:
When he was abused, he did not return abuse; when he suffered, he did not threaten; but he entrusted himself to the one who judges justly. . . . Therefore, let those suffering in accordance with God's will entrust themselves to a faithful Creator, while continuing to do good. (1 Pet 2.23, 4.19)