No new insight, but coming alive in a different way for me now:
To be wholehearted is to receive the whole of the world in my heart.
If my heart is open to some beings and not others, to some aspects of myself and not other aspects, to some situations and not other situation, it is split, broken, partially open, or open only part of the time. If my open heart is only available to some beings, aspects and situations, that means it is available to myself only partially, only some of the time. It is available only half-heartedly, including to myself.
If my heart is open for all beings, all aspects, all situations, it is whole. It is available wholeheartedly. It is available to myself wholeheartedly. With its sense of fullness, warmth, connection, passion, belonging, softening, healing, deepening, coming home.
Beliefs is the reason for half-heartedness. A person, aspect or situation arise, I see it as wrong, and close my heart off.
So inquiring into beliefs is one way to allow them to fall away and the heart to open. When it functions without the filter of beliefs, it is naturally open - available to anyone, any situation.
Another is to allow the person or situation into my heart, which in turns allows the belief to soften.