RESUMEN:
El bien es difusivo significa que el bien es causa final y en la medida en que el ser tiende a él, se perfecciona. También se puede entender que el bien creado es fin intermedio para otras criaturas en la medida en que refleja a su vez el ser de Dios. Varias citas del dominco Bernhard O.P.

TEXTUAL:
By placing the good primarily under final causality, Thomas removes the sense of necessity in self-communication. (...) The good is perfective of the whole being, while the efficient cause is that through which the good is attained. Good is predicated of final causality before efficient causality. p.825

The good is that for which an agent acts, its end or purpose. Applying this passage about God's goodness to creatures, we can say that the good's self-communication follows from the fact that the end of creatures is only attained through action, and action means the outpouring of goodness. Every action announces a substance's existence, its substantial goodness, and communicates some kind of accidental good as well, some accidental goodness or truth. p.825

We can understand this more deeply by looking to the principle that everything attracts its like. If the good moves something, this means that the thing moved is itself good. Hence, one good is moved to act in order to attain another good, to attain something like itself. (p.825).

(...) The good naturally attracts the subject. If the good is diffusive as an end that moves, then the good draws the subject towards operation and perfection, moves the subject to share its good in order to attain the actualization of its accidental powers. (p.826). (...)

These points allow us to conclude that created esse is relational, is necessarily acting upon other beings and being acted upon by them. 827

FUENTE:
BERNHARD O.P., BLANKENHORN: The Good as Self-Diffusive in Thomas Aquinas, Ed., 2002

FUENTE AMPLIADA:
BERNHARD O.P., BLANKENHORN: The Good as Self-Diffusive in Thomas Aquinas Ed. , , 2002