If you understand the universal preponderance of component/composite relations and how those relations give rise to variance and complexity, then you will understand how "compassion" is a composite behavioral repertoire with unique, emergent features and properties -- a behavioral cusp with associated pivotal response capabilities.
So how does this emergent behavioral repertoire evolve? What are its "necessary" elements? One is a generalized same/different repetoire of both emergent VBCs and their component behavioral elements. Another is a generalized verbal and non-verbal imitative repertoire (with emphasis on generalized prosodic variations and physical actions that evoke "compassionate" as a tact). This allows the individual to produce precise imitations of modeled "compassionate" behavior. Another is a generalized, public and private-event tact repertoire This allows the individual to verbally name what is the same and what is different between what is heard and seen and what is said and done. In this way an individual can determine how his or her behavior aligns or doesn't align with publicly modeled expressions of "compassion". This creates a feedback loop and such loops are foundational to the emergence of complexity, and a compassionate repetoire is a complex structure, a structure evolved from the interaction both direct-acting, material and indirect-acting verbal contingencies. An ancillary and necessary feedback loop is one that selects positive correspondance with a model over negative correspondance with a model. When the feedback loop selects negative correspondancw with a model it is ofter referred to as "recalitrance" or "obstinance".
In essence, a compassionate person is a person who can (1) tact the hierarchical relations that organize component behaviors into a combined repertoire of "compassionate behavior", (2) self-tact their correspondance between seeing/hearing and saying/doing, and (3) whose behavior is shaped by contingencies that select behaviors that correspond to positive exemplars of socially valued "compassionate" behavior.