Objection 1. It would seem that God cannot be loved immediately in this life. For the "unknown cannot be loved" as Augustine says (De Trin. x, 1). Now we do not know God immediately in this life, since "we see now through a glass, in a dark manner" (1 Corinthians 13:12). Neither, therefore, do we love Him immediately.
Objection 2. Further, he who cannot do what is less, cannot do what is more. Now it is more to love God than to know Him, since "he who is joined" to God by love, is "one spirit with Him" (1 Corinthians 6:17). But man cannot know God immediately. Therefore much less can he love Him immediately.
Objection 3. Further, man is severed from God by sin, according to Isaiah 59:2: "Your iniquities have divided between you and your God." Now sin is in the will rather than in the intellect. Therefore man is less able to love God immediately than to know Him immediately.
On the contrary, Knowledge of God, through being mediate, is said to be "enigmatic," and "falls away" in heaven, as stated in 1 Corinthians 13:12. But charity "does not fall away" as stated in the same passage (1 Corinthians 13:12). Therefore the charity of the way adheres to God immediately.
I answer that, As stated above (I, 82, 3; 84, 7), the act of a cognitive power is completed by the thing known being in the knower, whereas the act of an appetitive power consists in the appetite being inclined towards the thing in itself. Hence it follows that the movement of the appetitive power is towards things in respect of their own condition, whereas the act of a cognitive power follows the mode of the knower.
Now in itself the very order of things is such, that God is knowable and lovable for Himself, since He is essentially truth and goodness itself, whereby other things are known and loved: but with regard to us, since our knowledge is derived through the senses, those things are knowable first which are nearer to our senses, and the last term of knowledge is that which is most remote from our senses.
Accordingly, we must assert that to love which is an act of the appetitive power, even in this state of life, tends to God first, and flows on from Him to other things, and in this sense charity loves God immediately, and other things through God. On the other hand, with regard to knowledge, it is the reverse, since we know God through other things, either as a cause through its effects, or by way of pre-eminence or negation as Dionysius states (Div. Nom. i; cf. I, 12, 12).
Reply to Objection 1. Although the unknown cannot be loved, it does not follow that the order of knowledge is the same as the order of love, since love is the term of knowledge, and consequently, love can begin at once where knowledge ends, namely in the thing itself which is known through another thing.
Reply to Objection 2. Since to love God is something greater than to know Him, especially in this state of life, it follows that love of God presupposes knowledge of God. And because this knowledge does not rest in creatures, but, through them, tends to something else, love begins there, and thence goes on to other things by a circular movement so to speak; for knowledge begins from creatures, tends to God, and love begins with God as the last end, and passes on to creatures.
Reply to Objection 3. Aversion from God, which is brought about by sin, is removed by charity, but not by knowledge alone: hence charity, by loving God, unites the soul immediately to Him with a chain of spiritual union.
Source: Summa Theologica (New Advent)