"Rend your heart and not your garments." Joel 2.13
In the ancient world, tearing your garments was a means of expressing extreme grief, anger or repentance. It was costly, given the absence of cheap designer-fashion fuelled by slave-labour in oriental sweatshops. Many people only possessed one set of clothes and so, ripping them apart meant going naked, purchasing another set or, most likely repairing them. It might have been easier to sacrifice a month's salary, though not as dramatic.
Even so, the prophet Joel's demand to go farther and deeper by rending one's heart, rather than one's clothes, cuts to the core of God's own call on our lives... He is not fooled by outward gestures - however dramatic and/ or costly - he is looking for integrity, the order of change which transforms us from the inside out. Rending our hearts is about revisiting our most basic and integral assumptions and habits, with a view to changing what we previously took for granted.