I don't think that this is a mandate to go out and seek suffering, but more of an assured and inherant truth in being a Christian, for several reasons.
Firstly, we are told by Christ that no servant is greater than the Master, and that, if the world has hated the Master, so then they will hate the servant. If we are servants of Christ, then it is natural the world will hate us and cause us to suffer in all manners of ways. Suffering need not be sought, it can be had by merely going out into public as a professing Christian.
Furthermore, Christ has promised that he has not come to bring peace, but a sword. He will turn family against family and that, if anyone is worthy of following Him, he must forsake his family that have forsaken Him. This is not to say that everyone must cut ties from their family completely, but I would certainly say that this involves, to the least degree, at least some familial tension between believers and non-believers, and I myself would not give a second though to breakign ties to family who are openly hostile to Christ. Christ has assured us that because of Him, we will not have peace within our own households.
Also, and this is no minor issue, we have our stuggle with sin. While we are freed from sin, we are not free of sin yet and we still have our thorns in our side which will mourn us for the rest of our lives. This is no small sentence to us, due to the fact that these sins grieve us because it is a rebellion against our God, who suffered to save us from them.
The mere fact that we are Christians, means that we will suffer, some more than others, and in different ways. We need not seek it out though, and I think we are more assured to suffer, rather than commanded.
