"He then began to teach them that the Son of Man must suffer many things and be rejected by the elders, chief priests, and teachers of the law, and that he must be killed and after three days rise again."
Not even God's own Son could avoid suffering in this life, rather suffering must have been endured if sins were ever to be forgiven and God justified. What hope have we to avoid suffering and what right do we have to pretend we do not suffer? Surely as we were baptized into Christ's death and raised with him into eternal life, so too do we take part in the same sufferings that Christ suffered on our behalf.
We are not promised lives free of suffering, but we are promised the presence of the Eternal One who bears us up and comforts us when we suffer. So often is it said of God, "Why does this good God allow suffering?", but this same God brings grace to those who are unrighteous and compassion on those who deserve none. If God was unrighteous, then there is no salvation, but his righteousness has been revealed in Christ for all those who believe. If God could not justify the wicked, which we were, how then could he justify our existence?
For if not for God's forbearance and graciousness on us, we would have been wiped out at Eden. So why does God allow suffering? The same reason he allowed sinners (you and me) to exist, so that they might be able to come to repentance through his Son Jesus Christ.