I can't help but read this passage and think of the Danish Philosopher Soren Kierkegaard. In one of his influential books on the spiritual life, he talks about this undivided heart, committed to God. Without going into too much detail about the book, the name will suffice to make my point. The title of the book is, "Purity of Heart is to Will One Thing." Too often, we think of purity in the form of cleanliness or chastity or freedom from guilt, but it is so much more than that. Think of pure gold or silver. All of the impurities and contaminants have been removed. Think of a pure gem that is almost completely transparent and flawless. Think of water that has been completely purified for drinking.