"And he said to all, 'If anyone would come after me, let him deny himself and take up his cross daily and follow me. For whoever would save his life will lose it, but whoever loses his life for my sake will save it. For what does it profit a man if he gains the whole world and loses or forfeits himself? For whoever is ashamed of me and of my words, of him will the Son of Man be ashamed when he comes in his glory and the glory of the Father and of the holy angels.'" - Luke 9:23-26
Christians love to make their salvation about themselves: their decision to pursue it, their choice to accept it, their works to earn it. Thus when we hear this well known passage our gut reaction is to think of the taking up of one's cross as something we do to earn God's approval--to prove ourselves to Him. We look at the ways we suffer in our everyday lives and congratulate ourselves for persevering in the face of that suffering: "See, Jesus? See? I'm suffering but I'm not giving up. I'm following you. I'm remaining faithful. Aren't you proud of me?" We are perhaps tempted to buy into the Roman Catholic view of our suffering as something we can "offer up" to Jesus, adding our suffering to His so as to help Him in his redemptive work.
Here's what Father Luther has to say about that:
"Illness, poverty, pain, and the like must not be called a cross; they are not worthy of that name. . . . This is finding the cross: to know your own self, or to know the cross. Where do you find that? In your heart. Unless you find it there the finding of it outwardly is of no avail. 'Whosoever willeth to come to me, let him take up his cross and follow me.' You must come to the point when you say, 'My Lord and my God, would that I were worthy of it.' You must be as joyful about it as were the dear saints." (Martin Luther, Day by Day We Magnify Thee, Sermons from 1527)
So much for smugly patting ourselves on the back for enduring all that this world throws at us. None of that can even qualify as a cross. "This is finding the cross: to know your own self . . . ." In other words, finding the cross is looking within and seeing the sin that is responsible for our Saviour's taking up His cross and then being brought to repentance and wanting nothing more than to follow that Saviour in the way of the cross because that is where hope, forgiveness, and new life are to be found.
Jesus doesn't ask us to take up our crosses so that we can help Him. He asks us to do it so that He can help us.