According to this metaphor, in the case of the three core spiritual disciplines, fasting serves a catalyst, moving prayer to service, or alms-giving. Applied to the three transcendentals, Beauty is the catalyst, helping to transform Truth into Goodness. Of course the fundamental dynamism of reality is the Most Holy Trinity. If I were push this metaphor, which is really to do nothing other than economically schematize God, it seems to me that the Son is the catalyst.
Even Plato noticed, across many of his Socratic dialogues, that threeness, if you will, seems built into the structure of reality, most notably in his tripartate division of the human soul (i.e., pysche) in the Republic.
Stated simply, just as fasting helps turn prayer into service (i.e., diakonia) Beauty helps turn Truth into Good[ness]. Beauty also opens us to wonder, which is necessary to apprehend truth.