Richard Muller explains the Reformed orthodox doctrine of the gratia Dei as being a divine perfection:
Although by far the larger discussion of divine grace belongs to the soteriology of Reformed orthodoxy, the theologians of the late sixteenth and seventeenth centuries also consistently place the gratia Dei among the divine affections. Divine grace, as indicated both in the doctrine of the divine attributes and in the developing Reformed covenant theology of the seventeenth century, is not merely the outward favor of God toward the elect, evident only in the post-lapsarian dispensation of salvation; rather is it one of the perfections of the divine nature. It is characteristic of God’s relations to the finite order, apart from sin, in the act of divine condescension to relate to finite creatures. Beyond this, it is a characteristic of the divine being itself, at the very foundation of God’s relationship with finite, temporal beings.
~PRRD vol. 3 pg. 570
Muller even adds a footnote which says:
There is, both in the orthodox Reformed doctrine of God and in the orthodox Reformed covenant theology of the seventeenth century, a consistent identification of grace as fundamental to all of God’s relationships with the world and especially with human beings, to the point of the consistent assertion that the covenant of nature or works is itself gracious.
Now this is probably a point where Muller doesn’t discuss the “discontinuity” in Reformed orthodoxy. There were at least some Reformed thinkers who would have disagreed, though Muller gives the mainstream position. With the development of the covenant of redemption and high Calvinism, one wonders how it could be the case that grace is the fundamental ground of God’s relationship with all men.
But that’s a much larger discussion.