The whole value of the meditation of the suffering of Christ lies in this, that man should come to the knowledge of himself and sink and tremble. If you are so hardened that you do not tremble, then you have reason to tremble. Pray to God that he may soften your heart and make fruitful your meditation upon the suffering of Christ, for we of ourselves are incapable of proper reflection unless God instills it.
But if one does meditate rightly on the suffering of Christ for a day, an hour, or even a quarter of an hour, this we may confidently say is better than a whole year of fasting, days of psalm singing, yes, than even one hundred masses, because this reflection changes the whole man and makes him new, as once he was in baptism.
— Martin Luther
I came across it in Jesus, Keep Me Near the Cross, edited by Nancy Guthrie.
This is another book in the set alongside the advent edition that I quoted here.