I answer that, The number of the twelve fruits enumerated by the Apostle is suitable, and that there may be a reference to them in the twelve fruits of which it is written (Apoc. 22:2):  “On both sides of the river was the tree bearing twelve fruits.”  Since, however, a fruit is something that proceeds from a source as from a seed or root, the difference between these fruits must be gathered from the various ways in which the Holy Ghost proceeds in us:  which process consists in this, that the mind of man is set in order, first of all, in regard to itself; secondly, in regard to things that are near it; thirdly, in regard to things that are below it.

Accordingly man’s mind is well disposed in regard to itself when it has a good disposition towards good things and towards evil things.  Now the first disposition of the human mind towards the good is effected by love, which is the first of our emotions and the root of them all, as stated above (Q. 27, A. 4).  Wherefore among the fruits of the Holy Ghost, we reckon “charity,” wherein the Holy Ghost is given in a special manner, as in His own likeness, since He Himself is love.  Hence it is written (Rom. 5:5):  “The charity of God is poured forth in our hearts by the Holy Ghost, Who is given to us.”  The necessary result of the love of charity is joy:  because every lover rejoices at being united to the beloved.  Now charity has always actual presence in God Whom it loves, according to 1 John 4:16:  “He that abideth in charity, abideth in God, and God in Him”:  wherefore the sequel of charity is “joy.”  Now the perfection of joy is peace in two respects.  First, as regards freedom from outward disturbance; for it is impossible to rejoice perfectly in the beloved good, if one is disturbed in the enjoyment thereof; and again, if a man’s heart is perfectly set at peace in one object, he cannot be disquieted by any other, since he accounts all others as nothing; hence it is written (Ps. 118:165):  “Much peace have they that love Thy Law, and to them there is no stumbling-block,” because, to wit, external things do not disturb them in their enjoyment of God.  Secondly, as regards the calm of the restless desire:  for he does not perfectly rejoice, who is not satisfied with the object of his joy.  Now peace implies these two things, namely, that we be not disturbed by external things, and that our desires rest altogether in one object.  Wherefore after charity and joy, “peace” is given the third place.  In evil things the mind has a good disposition, in respect of two things.  First, by not being disturbed whenever evil threatens:  which pertains to “patience”; secondly, by not being disturbed, whenever good things are delayed; which belongs to “long suffering,” since “to lack good is a kind of evil” (Ethic. v, 3).