May I share a nugget from the book that I am currently reading (very slowly... it is very heavy and I often wonder if I have bitten off more than I can chew):

"... An important passage in this connection is Colossians 3:14. Here love is called "the bond of perfectness." We would probably be overstating the matter if we would call this a definition of love; yet it would seem to approach the nature of a definition. By "bond of perfectness" I understand a bond or union that is characterized by perfection in the ethical sense, such as truth, righteousness, and justice. According to this phrase, then, love is a bond that can exist only in the sphere of moral perfection. There is no love in the sphere of darkness. They who love darkness cannot love one another in the true sense.

Love is profoundly ethical. If, as we have gathered, love is the bond or fellowship that is caused by the mutual delight of two parties in each other, by their longing for each other and seeking after and finding of each other, then we learn from Colossians 3:14 that the cause of this delight and longing must be found in the ethical perfection of the loving parties. He who loves in the true sense has his delight in ethical perfection, in moral goodness, and in truth and righteousness, and he moves in the sphere of the light. Both he who loves and he who is loved must be perfect. Since love is the bond of perfectness, it is the bond that unites ethically perfect parties only. Love is an ethical and, therefore, a personal virtue. It can exist only between personal beings, and these personal beings must be perfect.

It is true that the word is used in Scripture as referring to the very opposite of ethical perfection for its object when Scripture speaks of men who love darkness rather than light (John 3:19) and who love the glory of men more than the glory of God (John 12:43). But this merely emphasizes the perversion of love in the natural man, even as it is not love, but adultery, when a husband is unfaithful to his wedded wife and is said to love another woman.

...
We may define love as the spiritual bond of perfect fellowship that subsists between ethically perfect, personal beings, who, because of their ethical perfection, have their delight in, seek, and find one another. The love of God is the infinite and eternal bond of fellowship that is based upon the ethical perfection and holiness of the divine nature and that subsists between the three persons of the holy Trinity."

(from Herman Hoeksema, Reformed Dogmatics, Vol. 2, pp. 151-153)

If what Rev. Hoeksema says is correct, then love is not strictly an attribute of God but a perfect state of fellowship within the ethically perfect (holy) persons of the Godhead. Alternatively, it can be regarded as a secondary attribute of God, because its definition depends on the the primary attribute of holiness.

That would explain why God presses the pre-eminence of holiness; if we are not holy, we cannot love or be loved in the strictest sense.

In this was manifested the love of God toward us, because that God sent his only begotten Son into the world, that we might live through him.