Objection 1. It seems that God loves all things equally. For it is said: "He hath equally care of all" (Wisdom 6:8). But God's providence over things comes from the love wherewith He loves them. Therefore He loves all things equally.
Objection 2. Further, the love of God is His essence. But God's essence does not admit of degree; neither therefore does His love. He does not therefore love some things more than others.
Objection 3. Further, as God's love extends to created things, so do His knowledge and will extend. But God is not said to know some things more than others; nor will one thing more than another. Neither therefore does He love some things more than others.
On the contrary, Augustine says (Tract. in Joan. cx): "God loves all things that He has made, and amongst them rational creatures more, and of these especially those who are members of His only-begotten Son Himself."
I answer that, Since to love a thing is to will it good, in a twofold way anything may be loved more, or less. In one way on the part of the act of the will itself, which is more or less intense. In this way God does not love some things more than others, because He loves all things by an act of the will that is one, simple, and always the same. In another way on the part of the good itself that a person wills for the beloved. In this way we are said to love that one more than another, for whom we will a greater good, though our will is not more intense. In this way we must needs say that God loves some things more than others. For since God's love is the cause of goodness in things, as has been said (2), no one thing would be better than another, if God did not will greater good for one than for another.
Reply to Objection 1. God is said to have equally care of all, not because by His care He deals out equal good to all, but because He administers all things with a like wisdom and goodness.
Reply to Objection 2. This argument is based on the intensity of love on the part of the act of the will, which is the divine essence. But the good that God wills for His creatures, is not the divine essence. Therefore there is no reason why it may not vary in degree.
Reply to Objection 3. To understand and to will denote the act alone, and do not include in their meaning objects from the diversity of which God may be said to know or will more or less, as has been said with respect to God's love.
Source: Summa Theologica (New Advent)