I'm hesitant to say CVT took it from Idealism or Hegel because some of his defenders, upon hearing the word "idealism," think I am saying he was an Idealist. I am not saying that. That said, yes, he borrowed it from Idealism. When you read him on Idealism, pay attention to the names Bradley and Boussanquet. The following discussion references Tseng's book on Hegel.
Substance metaphysics says that universals are defined (or determined) by their abstract forms. Not only is such a process mechanical, it is empty. The abstract form of cat does not exist the way this cat does (87). When Hegel says abstractions do not exist, he is not a nominalist. Take the sentence
“This cat is small and that cat is big.” Each cat is an abstract particular. Having gotten our unity by generalizing, “by abstracting from particulars in order to include them into larger unities,” we have emptied these universal forms of any real definable content (Van Til). What Hegel (and Van Til) suggest is a concrete universal.
A concrete universal, then, “is conceptually comprehended as absolute spirit as a concrete living substance” (Tseng 89). It is “the organic unity of every particular thing, and it makes every particular meaningfully related to all others.”
That helps, but it is not the clearest. Here is my tentative effort. Instead of seeing “this cat” as an exemplar of the form “Cat-ness,” “this cat” is now a focal point to the universal reality of cat. Quite so, but what is the payoff for Van Til? Van Til wants to see the Trinity as a concrete universal. This might work, but Van Til’s often sloppy language prevents it from fully working.
As such, a divine person would be the particular that “fully exhausts” the divine essence. Perhaps, but one has to be careful in seeing a divine person as a “particular.”