/summa/SS/SSI/SS_Q28:
WE must now consider the effects which result from the principal act of charity which is love, and (1) the interior effects, (2) the exterior effects. As to the first, three things have to be considered: (1) Joy, (2) Peace, (3) Mercy.
Under the first head there are four points of inquiry:
(1) Whether joy is an effect of charity?
(2) Whether this kind of joy is compatible with sorrow?
(3) Whether this joy can be full?
(4) Whether it is a virtue?