That verse took on a new meaning for me today.
It happened because I'm studying some material by Ariel & Shya Kane about living in the moment.
They are passionate about the concept of being present in your own life, because you are either living your life, or thinking about your life. You can't do both at the same time. You miss your own life if you become preoccupied.
So in that context, what does loving the Lord with all your heart, all your soul, and all your mind mean? Bringing all of your attention to God when you love Him.
It's just like when we talk to a loved one, we want all of their attention at that time. We want the gift of the whole person engaged with us in that moment.
Love the Lord your God with all your heart, all your soul, and all your mind.