Human life is full of variation
When we are young, we go to school and we look forward to the holidays. Afterwards, we start looking for a job, and when we are lucky enough to find one, we have our work to attend to. There is our family life, our contacts with friends, the media, etc. So many things draw our attention that it is quite possible to live outside ourselves, at the surface, without being truly ourselves.
Often we have to get into some kind of personal trouble before we start sorting ourselves out. what do I really want? What is really good? What should I be doing?
As long as we have not asked ourselves such questions, we are drifting along, and our life has no heart because we have not yet learned to listen to our own heart. We are still in exile. To live authentically as a person, to become our true selves, we have to draw on those inner resources, which God has given us: self-awareness, some light within, our deepest longings, our conscience, our hope.
This is what Holy Scripture calls our 'heart'. In our times, we may speak of the core of the person, our inner self, interior life, spiritual life; but also the word 'heart' is still frequently used in its deep sense.