HR, high priests, and sausage rolls.
Humans are ceremonial creatures, we naturally mark transitions with ceremony and ritual. From something as simple as a birthday all the way to a wedding or a graduation.
It is very difficult, near impossible, for us to move into the next stage of life without ritual.
Unfortunately, our organisations are ritual poor. On-boarding is perhaps a series of emails (or worse, pdfs), and leaving organisations happens quietly and often without any ceremony (maybe a cheap platter from your local grocery store and a couple of forced thank-yous, sausage roll anyone?).
If you want your people to truly belong, to truly 'on-board', to truly embody the culture of your organisation you need to tap in the ancient power of ritual and ceremony.
In short, your head of HR needs to function more like a high priest.
Pierre