You don't shower or do laundry once and call it good for the rest of your life (ahhh, but wouldn't that be nice?!). In the same way that it's necessary to wash our bodies and our clothes on a regular basis in order to make them clean, it's critical for us to wash ourselves spiritually by spending time in God's Word. Through Christ's blood, we can be washed white as snow, but it's up to us to keep up on our daily "hygiene".