It is possible to be very devout; meticulous in every detail of one's religious tradition, and be worshiping something other than God. In this case, the object of Israel's devotion is the devotional exercises themselves. Instead of enabling and assisting them in placing their lives at God's disposal, these pious routines are really instruments to put God at their disposal. No wonder God appears to speak so sarcastically.
I'm busy working on my blog posts. Watch this space!