[St. Thomas beings to consider the various degrees of divine love possible to creatures. Having shown that only God can love God as much as he deserves to be loved, he concludes that the only mode of loving God perfectly that is possible for a rational creature, is that which is taken on the side of the one who loves, namely that the rational creature love God with his whole power; [and love that is perfect in this way is the love we are commanded to have] hence this is also expressed clearly in the precept of divine love. For it is said in Deut 6:5, "You shall love the Lord your God with your whole heart, and with your whole soul, and with your whole strength," and in Luke 10:27 it is added, "and with your whole mind"; heart may be referred to intention, mind to knowledge, soul to affection, strength to execution. For all these things are to be given over to the love of God. But it should be considered that this precept may be fulfilled in two ways. For since "whole" and "perfect" is that to which nothing is lacking, one loves God with the whole heart, soul, strength, and mind, if nothing of these fails to be actually turned wholly towards God. [Again a distinction regarding ways of being totally given over to love. In the fullest sense, to be totally given over to love means that at every moment, every power and act of ours is fully informed by love.]
This perfect mode of love does not belong to wayfarers, but only to those who enjoy beatitude. Hence the Apostle says, "Not that I have already obtained this or am already perfect; but I press on to lay hold of it" (Phil 3:12), as though expecting perfection when he laid hold of the palm of beatitude. But he does not take "laying hold" insofar as it implies comprehending or enclosing, for in this sense God may not be comprehended by any creature, but insofar as "laying hold" implies attaining that which one has followed and sought after. [As St. Paul remarks, we will only be truly perfect in heaven, while here we aim for that goal.] For in that heavenly beatitude the intellect and will of the rational creature shall always be borne actually towards God, since beatitude consists in the enjoyment of God, and beatitude does not consist in habit, but in act. And since the rational creature will cling to God, who is Supreme Truth, as its last end, and all things are referred in intention to the last end, and all things to be done are arranged according to the last end as according to a rule, it follows that in the perfection of beatitude the rational creature will love God with its whole heart, since its whole intention will be borne to God in all that it thinks, loves, or does; with its whole mind, since its mind will always be actually borne towards God, always seeing him, and judging all things and about all things in him and according to his truth; with its whole soul or its whole strength, since the love of God will be that which arranges all external acts. This is then the second mode of perfect divine love, which belongs to the blessed. [It is due to the imperfection of our human nature that after we decide to do something, and begin thinking about how to do it, we are no longer thinking as distinctly or vividly about the goal; similarly that when we are doing all the particular daily tasks of a life devoted to one's family, or ultimately, devoted to God, our heart is often turned to those tasks, being distracted either by enjoyment of them or by displeasure or annoyance from them. But since this is only from our weakness, not from an inherent contradiction in loving the person to whom we are devoted, and giving attention to the particular things we're doing at the moment, when God totally fills our mind and heart with his presence, as he will do in heaven ("the Lord God will be their light" {Rev 22:5}), then love for him will pervade each and every one of our particular thoughts and actions.]