Grace implies more than relationship, however, it implies the way we come to know God, and there are various levels of knowledge, to which I shall return in this series later. Intuition is one way.
Let me quote Garrigou-Lagrange again:
Sanctifying grace, which is far superior to the angelic nature, is an analogical likeness to God inasmuch as He is God, or to His Deity, to His intimate life, which is not naturally knowable in a positive way. This is why, above the kingdoms of nature (mineral, vegetable, animal, human, angelic), there is the kingdom of God: the intimate life of God and its formal participation by the angels and the souls of the just.
Therefore to know perfectly the essence or quiddity of grace, one would have to know the light of glory of which it is the seed, just as one must know what an oak is to know the essence of the germ contained in an acorn. But it is impossible to know perfectly the essence of the light of glory, essentially ordered to the vision of God, without knowing the divine essence immediately by intuition. Hence St. Thomas declares, in demonstrating that only God can produce grace, Ia IIae, q. 112, a. 2: “It must be that God alone should deify, communicating a fellowship in the divine nature by a certain participated likeness, just as it is impossible for anything but fire to ignite.” The word “deify” shows that grace is a participation in the divine nature, not according to the reason of being or intelligence merely, but by the essential, intimate reason of Deity.